Bottlehead Forum
Bottlehead Kits => Legacy Kit Products => Paramount => Topic started by: galyons on March 14, 2014, 09:30:27 PM
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I am buying a pair of original Paramounts w/300B's. I will need to rework them because the original build was poorly done and the cosmetics are more than tired.
PJ mentioned several times in the old and new forums that his plan was to take the drivers to 6SN7's on his. That would be my preference as well. But I could not find any needed circuit changes for the original 12AT7 driver boards in my forum searches.
I also plan to implement the B+ switch on the PS board, (switch on the exterior), as described on the forum by PJ:
“For the stock Paramount in 2A3 configuration (direct coupled), we have seen no problems with old stock 2A3s, or with the supplied Sovtek tubes. A few modern-production tubes have shown a visible and/or audible arc and "pop" through the speakers; this has been known since the ParaGlow days (predecessor to the 2A3 Paramount) and the usual solution was to implement a standby switch on the high voltage supply - or use a tube that does not have the problem. This is, incidentally, why the Paramount power supply circuit board has a place for that high-voltage switch - it's not mentioned in the manual where a jumper closes the circuit, but the jumper is in the circuit at a place where a normal 240vAC switch can be safely used to switch on the high voltage.â€
My reading of the information on the softstart V1.1 upgrade is that it is primarily to accommodate 2A3's being directly coupled and the 5760 driver. (I like the 5760 and have them in a non-BH headphone amp, but have too many 6SN7 & 7N7 tubes to not use them!)
So the change to octal/loktal and the B+ switch should get me everything that I want/need. (I have Paramour 45's w/ MQ iron and Paramour 2A3's with Altec OPT's, (yeah I know, maybe a couple too many P's!)) If I decide to give up the 300B’s down the road for 2A3’s, then I would definitely do the soft start, but maybe leave the driver as a 6SN7 or 7N7.
PJ said to post so the information would be available to the forum. His initial response was:
“ The pinout of the 6SN7 is obviously different :^) but other than that the SS board should work. You'll be adjusting for something around 6 volts bias on the driver section instead of 4v on the 5670, but the range is 2.5 to 7.5 volts so there should be no problem.
I do definitely recommend the SS board for any direct coupled version, 2A3 or 45. The ability to adjust the driver plate voltage is very important to get the best out of the design, and was left out of the original Paramount only because it repeated the legacy (Afterglow/Paraglow) design as closely as possible.
I haven't done it myself yet, so no direct experience. But I'll help out on the forum.â€
The old driver boards for the 12AT7 don't have a trim pot, but it looks like the current requirements are close for the 6SN7, as well. Will there need to be resistor or other changes to the old boards to make them work with 6SN7's?
I will start the rehab on the amps early next week. Will need a few days to get them running to original spec's with the 12AT7's. Then switch out the 9 pin socket for an 8 and let the games begin!
Cheers,
Geary
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Hi Geary,
I can't speak to the old boards but on the new it was as easy as plugging it in and adjusting the bias pot. You are going to loose a lot of gain going from the 12AT7 to a 6SN7, something like 12dB. Give the 12AT7 a shot, you may like it.
Regards,
Aaron
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What operating point do you use for the 6sl7?
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Hi Geary,
I can't speak to the old boards but on the new it was as easy as plugging it in and adjusting the bias pot. You are going to loose a lot of gain going from the 12AT7 to a 6SN7, something like 12dB. Give the 12AT7 a shot, you may like it.
Regards,
Aaron
Thanks Aaron,
I have AT7 family tubes in my Paramours. It is not that I don't like AT7's, I do. But the 6SN7's are just a bit nicer to my ears...sweeter..better timbre...better imaging. I don't need all of the AT7's gain as I use a preamp.
I haven't changed out the AT7's in the Paramours for octal/loktal because I don't want to permanently enlarge the socket hole, (and I am not a big fan of the adaptors). I have considered changing the pin outs in the Paramour 45 for 6CG7's. (has the PT with higher heater current). Just haven't pulled them out of the system to do so.
The Paramounts are designed for 8 pin sockets so that makes the decision that much easier! (And PJ's seemingly constant tease about doing so on his! ;) )
Cheers,
Geary
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What operating point do you use for the 6sl7?
Xavier, part of my desire is to reduce the gain on the Paramounts, so 6SN7's rather than 6SL7's. The plate current is about the same as 12AT's. It think it is the bias that I may need to tweak and I am seeking guidance to do so.
Cheers,
Geary
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You're right. 6SL7s. Aaron, what voltage you adjusted the trimpot for? You used the same bias as the 12at7?
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I had a thread on this a while back. Keep the bias per the specs. For the 300B amp this is 175v with the SS version. PJ recommended changing the trim pot from a 10k to 20k but I have plenty of range with the stock pot.
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Thks
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I had a thread on this a while back. Keep the bias per the specs. For the 300B amp this is 175v with the SS version. PJ recommended changing the trim pot from a 10k to 20k but I have plenty of range with the stock pot.
Please bear in mind, this amp is not V1.1 with soft start. This is the original Paramount with the 12AT7 driver boards, no trim pot.
Cheers,
Geary
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Hello Geary,
I would strongly suggest going with the Soft-Start PCB's instead of the high voltage switch if at all possible. If you plan to stay with 300B's, the Soft-Start feature and the high voltage switch will be unnecessary.
Using the soft-start PCB's, you'll have room for heatsinks on the MJE5731A's, and the adjustable driver bias trim is extremely useful if you plan to convert to 2A3's in the future.
If you're willing to add a hole, I'd advocate trying the 6GK5 as a driver tube, then use a 6SN7 or 6J5 in an octal socket as the shunt reg tube. You could also run the 3S4 as a pentode driver with some additional tweaking.
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Thanks PB!
I would strongly suggest going with the Soft-Start PCB's instead of the high voltage switch if at all possible. If you plan to stay with 300B's, the Soft-Start feature and the high voltage switch will be unnecessary.
The plan is to stay with the 300B, at least for now. I have tried 300B's in the past, and go back to 2A3/45's. So if I do go 2A3's, yes, I would consider it imperative to get the new board.
Using the soft-start PCB's, you'll have room for heatsinks on the MJE5731A's, and the adjustable driver bias trim is extremely useful if you plan to convert to 2A3's in the future.
Although I don't have the amps in my possession, (tomorrow evening I will), there are heatsinks on the MJE350's.
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FUmYf0LN.jpg%3F1&hash=b0b256dfaf3794d49b965874ee035a9ad9f8fc17)
If you're willing to add a hole, I'd advocate trying the 6GK5 as a driver tube, then use a 6SN7 or 6J5 in an octal socket as the shunt reg tube. You could also run the 3S4 as a pentode driver with some additional tweaking.
You're killing me! ;D I have quite a few 6J5 metal and the usual "Quickie nut" bin full of 3S4's. I thought about a 76 as the driver and a 6J5 or 7A4 as the shunt regulator. I just hate to drill socket holes in the top plate to accommodate.
Cheers,
Geary
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Alright, if the driver boards are operational, I believe you will want to:
1. Install 431 Regulator on the empty side
2. Install 2.49K resistor in R3
3. Install 3.5K resistor between the bigger "+" pad (fed from Rc) and the left-most R4 pad (resistor stands up vertically)
4. Wire jumper from "K" to hole on Rc that feeds "+"
5. Wire jumper from "-" to "-" on other corner of PCB
6. Empty "+" pad goes to driver stage cathode
If you want to keep things somewhat easy, you could adjust the heater wiring and try a 6CG7 first, ensuring that the PCB's work, then do the gut and resocket.
-PB
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In PB's post, he suggested 2.49K and 3.5K resistors to create the 6v bias. In the soft start, those are a 4.99K resistor and a 10K trimpot - the old boards are not designed to take a trimpot.
I got the 6v value by reading the published curves by eye - no measurements were made, so no promise that I read the curves right! There is a likely +/-30% variation in plate voltage from tube to tube as well. That's why the trimpot is essential for direct coupled applications.
Some have remoted the trimpot for greater convenience. For anyone contemplating this, a few cautions - the wires must be twisted together and a non-inductive pot (not wirewound!) used, since this resistance is in the chip's feedback loop and it is prone to oscillate unless care is taken. I would use shielded twisted pair with the shield grounded to the chassis at the pot end to minimize noise or hum pickup at this sensitive node.
Just to clarify, the new board is larger primarily to accommodate a larger heat sink, the Aavid 5793. There were a few problems with the earliest version using MJE350s and no heat sink, and I wanted this board to handle a wider variety of applications.
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Alright, if the driver boards are operational, I believe you will want to:
1. Install 431 Regulator on the empty side
2. Install 2.49K resistor in R3
3. Install 3.5K resistor between the bigger "+" pad (fed from Rc) and the left-most R4 pad (resistor stands up vertically)
4. Wire jumper from "K" to hole on Rc that feeds "+"
5. Wire jumper from "-" to "-" on other corner of PCB
6. Empty "+" pad goes to driver stage cathode
If you want to keep things somewhat easy, you could adjust the heater wiring and try a 6CG7 first, ensuring that the PCB's work, then do the gut and resocket.
-PB
Thanks PB! I like the idea of 6CG7 first, after installing the modified driver boards.
Is this an accurate "pic" of your scheme? (Corrected per PB) Leave everything on "A" the same? Populate the rest of "B" per manual?
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FOFeU0Ke.jpg&hash=97088df9e7fc35622e5b79c5ee3aed7579a74b6d)
If so, I'm on it. I'll have to get a couple of the LM413's, but have the resistors.
Cool! I'm excited.
Cheers,
Geary
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In PB's post, he suggested 2.49K and 3.5K resistors to create the 6v bias. In the soft start, those are a 4.99K resistor and a 10K trimpot - the old boards are not designed to take a trimpot.
I got the 6v value by reading the published curves by eye - no measurements were made, so no promise that I read the curves right! There is a likely +/-30% variation in plate voltage from tube to tube as well. That's why the trimpot is essential for direct coupled applications...
PJ,
Given the +/- 30% swing possible in plate voltages, then in my capacitive coupled scenario I should be OK? (OK = close enough for jazz) Or do you think I should try to get a trim pot wired in?
Cheers,
Geary
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Yeah, cap-coupled with the 300B, you'll be OK.
Your drawing is correct, except that the jumper to "K" should be on the solder pad on the edge of the PC board (which you'd undoubtedly do once the board had the 431 in it).
-PB
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Yeah, cap-coupled with the 300B, you'll be OK.
Your drawing is correct, except that the jumper to "K" should be on the solder pad on the edge of the PC board (which you'd undoubtedly do once the board had the 431 in it).
-PB
Glad you mentioned that! I was already looking for a sharp 1/2" drill bit to enlarge the solder hole!! ;)
Here is a corrected drawing. I noted and changed the original, as well.
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FOFeU0Ke.jpg&hash=97088df9e7fc35622e5b79c5ee3aed7579a74b6d)
Thanks for all of the help!
Cheers,
Geary
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From Stereomour thread:
There is a pattern. The guys with high sensitivity speakers are hearing the hiss. Owners of lower sensitivity speakers don't seem to be noticing it. Noise issues are not all or none, it's more a matter of degree. So what we can say is that we will do what we can to find a chip with a consistently lower noise level. But if you have really sensitive speakers and you hear noise that bothers you, you may have to use the alternative approach we have offered here anyway. That is the one of trade offs - along with reduced bandwidth - that you have to deal with when you go to very sensitive speakers.
I am not going to panic!!! I have 102dB/1w/1M horn speakers. I ordered the LM413's from Digikey. They will be here tomorrow. They are Fairchild LM431ACZ, so if I read the thread in Stereomour correctly, http://bottlehead.com/smf/index.php/topic,5828.0.html (http://bottlehead.com/smf/index.php/topic,5828.0.html) , I should be OK?
...So I called last week and Eileen sent me three new 431s to try. I tried all three in the channel with the hiss, and it still remained. Also, I even tried one of these new 431s in the silent channel and guess what: hiss was introduced where it wasn't before. I took a closer look at the markings on each and found that the original two that came in my kit were different: fKB31 LM431 ACZ (silent channel) and WS TL431A 12427 (hiss channel). Also, the three that were sent as the replacements were all the WS TL431A 12427 as well. My conclusion: I agree with your previous assumption that these different 431s are the hiss problem possibly due to manufacturing.
My next step will be to bypass the 431s with resistors as instructed in your previous reply, but what tolerance, voltage, etc. of 680 ohm resistors should I get? What specs on those very resistors should I stick to to have a successful outcome?...
I have one monoblock up and running. ;D The other will be up by the weekend. Looking to do the driver board mods to go to 6CG7, then 6SN7 shortly thereafter.
Cheers,
Geary
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The white noise or hiss will drive you a little nutty at first. After a few weeks you'll realize that the music is sublime and forget about it. :). I too would like a dead quiet circuit but the quality of sound is worth the added noise, at least for me.
I need to add that I moved from 100 dB sensitive to 95 dB and it still bothers me from time to time. That is, until I hit play :)
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I don't think the markings are a reliable indicator of performance. We'll know more in a few weeks after we've tested a variety of sources.
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Thanks Paul. I should have everything to do the board mods by this weekend. It will be interesting to see if the Digikey/Fairchild LM431's are hissy. Is so, I hope there will be a resistor alternative.
Cheers,
Geary
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The white noise or hiss will drive you a little nutty at first. After a few weeks you'll realize that the music is sublime and forget about it. :). I too would like a dead quiet circuit but the quality of sound is worth the added noise, at least for me.
I need to add that I moved from 100 dB sensitive to 95 dB and it still bothers me from time to time. That is, until I hit play :)
Aaron,
I agree. My system is not dead quiet, too many tubes! My listening position is about 12' from the speakers. Nearly dead quiet from there. Up close to the equipment & speakers there is low level tube rush.
Cheers,
Geary
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Working on driver board #1. Everything in. 9 pin socket rewired for 6CG7. Just a point of clarification. I will need to pull the current lead from "A" side K from B8 and replace it with the new lead from "B" side K via "+" to B8, yes?
Thanks,
Geary
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Yeah, this is where support will get a little lean.
The power supply regulator has the 431 with fixed resistors. The "K" pad from this portion of the PCB, and the "O" pad that feeds the "+" linked to that 431 (should be "OA") need to hit the same half of the 6CG7 (1,2,3 or 6,7,8).
The driver stage will take the lower current "O" pad (OB most likely) and the K from the adjustable half of the board.
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Yeah, this is where support will get a little lean.
I understand. So the current fact is I now have 3 LM431’s in possible play.
LM431 -(1), is on the 9 pin socket, going from the center post, (ground) to B3 cathode.
LM431 -(2), was already on the driver board “A†side and is, before any changes, going to B8 cathode.
LM431 -(3), I added to the driver board “B†side along with the 2.49K @ R3 and 3.5K @ the outboard end of R4 & the inboard larger + pad. The new lead goes from the smaller, outboard + pad.
The power supply regulator has the 431 with fixed resistors. The "K" pad from this portion of the PCB, and the "O" pad that feeds the "+" linked to that 431 (should be "OA") need to hit the same half of the 6CG7 (1,2,3 or 6,7,8).
If I understand correctly, this is LM431 (2). Then this circuit remains unchanged and the wire from KA remains on the cathode B8.
The driver stage will take the lower current "O" pad (OB most likely) and the K from the adjustable half of the board.
So here is where we need to check my understanding. The added LM431 (3), 2.49K & 3.5K resistors are to change the driver cathode bias from 2.5v to 6.0v. If that is correct, then the new lead from "B" side K via "+" would go to B3.
Do I then need to remove the currently installed LM431 (1), (from the center post to B3)? Then wire the new lead from the new circuit with LM431 (3) to B3 to provide the 6.0v bias?
Or? Leave LM431 (1) in place, as is and add the new circuit lead to B3 and the combined old and new LM431 (1+3) will give me the desired 6.0v cathode bias?
OR? Just grab the closest bottle of Scotch and enjoy the Paramour 45's and try thinking again tomorrow!? ;)
Thanks for hanging in with me on this!
Cheers,
Geary
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The 431 on the socket needs to be removed - it is superseded by the 431 that you're adding to the PC board.
-PB
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Perfect. So once I do this all of the test voltages will remain the same, excepting:
B3 will now be 6.0v instead of 2.5V and
B9 will be 0 instead of 3.1V.
I am still waiting for parts to finish the second board. Maybe tomorrow? Will report when I am up and running.
Thank you for all of the support and guidance. Gotta go find that Scotch!!
Cheers,
Geary
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Yeah, no doubt you may run into other oddities, just be sure to take your time and let us know if something isn't quite right.
-PB
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Thanks PB. I am stalled until Monday or Tuesday. Still missing a couple of parts.
I'll have to tough it out with the Paramour 45's until then!!
Cheers,
Geary
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Geary, I'm looking forward to your comparison of the 6CG7 and the 6SN7. I have a stash of the former but am quite happy with the later at the moment. Good luck with your project!
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One amp is done!! Now I always thought that PB was perfect!! Well, he is not!! He clearly stated, earlier in the thread, that I would see bias rise from 2.5V to 6.0V on the B3 of the 6CG7. Not so! It is only 5.999V on my meter. ;D (I won't mention that the closest to the 3.5K resistor, (on the added LM431), I could get was 3.47K ohms!)
So the changes to the bias voltage were spot on! I did get close to 12v on the other cathode, B8. That is double the approximately 6V in the manual, but seems to follow doubling the bias voltage on C3?
Hard to judge the sonic effect, too soon and only mono. BUT, it sounds really nice, smoother, perhaps a little bit better HF extension. This is with an EH gold 300B. Will try my "good" non test 300B's after all is sorted.
Big plus, my system really likes the reduced gain. I will have to rework the resistors in my FP3X potentiometer circuit. So initial report....Yeah man!
The change to 6SN7/7N7/6CG7 works!! As a matter of fact, it works very well! Thanks PB & PJ!! PB is helping me on an issue with amp 2, but hope to be back to 300B stereo quite soon.
Cheers,
Geary
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I'm glad to hear that you have one up and running, now you have a good reference point.
The 12V on the regulator Kreg is just where the cathode sits with the regulated B+ and the regulator triode drawing off the extra current provided by the "A" side C4S. Very, very generally speaking, more voltage gain=less voltage here, and less voltage gain=less cathode voltage. The voltage at that point must be above ~3V for the regulator to work, and once it's over about 30 volts, the regulator will pop, so there is a nice range of functionality.
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I have had about three weeks of listening to the Paramounts with PB's driver tube bias mod to run 6CG7/6SN7/7N7 tubes. I am quite happy with the sound. I am currently using 6CG7's because that was the simplest, most expeditious route to getting the amps running. Bear in mind that this is NOT a comparison to V1.1 with 5760 Softstart. I haven't heard that configuration. My goals were to lower driver stage gain and use 6SN7ish tubes. Mission accomplished!
I have compared this configuration to my Paramour 2A3's and 45's. The 45's are tricked out with MQ BCP-15 plate chokes and EXO-045 Nickel parafeed OPT's. The 2A3's have BCP-15's and Altec Lansing OPT's. The Paramounts are stock iron. All of the amps are capped with PIO and Teflon caps in the signal stages. The 45's have been my prime amps for awhile. The mid range is magical with a palpable presence that is simply eerie. The Paramounts get close to the midrange while besting the 45's in low and high frequency extension. The 2A3's were closer to the Paramounts but were bested across all subjective parameters.
My speakers are a reworked '60's 3 way horn system with 102dB/1W/1m sensitivity. Preamp is an FP3 Extended with 6cg7's. I could easily live with any of the three amps, but the Paramounts, with the more "ballsy" sound, really make the speakers shine with a broader array of musical genre's than the 45's. I listen to mostly jazz, blues, female vocals and classical. The Paramounts get the job done very well on all genres, where the 45's were challenged with big orchestral classical and some of the higher energy blues recordings. I have been listening to Shuguang 50 Year Treasure black bottles and Russian Genelex Gold Lion 300B's. Hard to say which I like better. Either set sounds damn fine with only rather subtle differences.
The reduced gain is really a blessing. I was never getting past about 6 clicks, out of 24, on my stepped attenuators. Listening range now is 10-14 clicks with real steps getting there! Now I may even be able to eliminate the dropping resistors before the selector switch. The system just "likes" the newly reduced gain MUCH better!!
So now, as is ALWAYS the problem, I am now dreaming of MQ iron upgrades for the Paramounts!!! But next step is to tear the amps apart, anodize the top plate, paint the PT's and generally clean up some rather dodgy cosmetics. That will be the switch over point for the octal/loktal tubes. Until then, I am a happy listener!!
My thanks to PB & PJ for helping me get this done!!! (And the Queen, too!)
Cheers,
Geary
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Hello Geary,
Do bear in mind that those resistors in the foreplay keep the input impedance reasonable.
If you remove them, you will need to replace the stock level controls with new ones (50-100K)
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Thanks Paul. I am running 100K attenuators and have 200k's as the dropping resistors. Never really been comfortable with this configuration, but it worked to get the gain down to somewhat usable. The attenuators are 0-75dB, so should be fine without the dropping resistors. (?)
Cheers,
Geary
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Ah, good, yeah, you may find that you no longer need them.
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So, how much different would these changes be in order to use the 6cg7 in the paramount 1.1 with soft start? Amps are not built yet, but SS boards are. If this is doable without major surgery to the SS board, then can I also assume that the 6sn7 will also work in much the same way?
Thanks,
Jim
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The 6sn7 is a drop in with a converter. I bought a pair off of ePay and didn't need to change a thing. Set the bias the same as you would for the 5670 at 175v.
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Thanks Aaron,
Since I haven't eeven drilled the top plate yet, it's just as easy to drill for an octal socket. Also easier for me to solder to. But this is great information.
Thanks,
Jim
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It you haven't heard the 5670, please give it a try. I've got a stash of them if you don't want to try and track them all down. If the 5670 doesn't cut it for you and if you can spare 6dB in gain then I would recommend trying the 6SN7. I've had the Paramounts with 12at7's and 5670's. For my system the 6sn7 was a better fit.
The spacers that come with the soft start kit will give you room to start with a 9 pin socket and later change to an 8 pin if you like. You are smart to over drill in the beginning. The socket is an easy rewire and I wouldn't lose too much sleep over that.
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I still plan to use the 5670 2c51 in my Paramour II 45. I have plenty of them too, including a NOS matched pair of Bendix Eclipse 2c51s.
The only ones I don't have are early 50s WE 396s and the siemens/ericsson 1950s black plate, gold pin 2c51s.
I'm also playing a hunch, based on experience, that the 6sn7s will play nicer with my speakers for my taste.
WAlso, nothing is set in stone yet, and it really depends on how the break-in on the speakers goes -- they're very, very nice, but also very articulate and detailed yet they are also good at showing the character of the gear in front of them, so a warmer, more lush front end will sound very much like that with these speakers and likewise, sterile, an anylytical front end will sound that way at the speakers. That may seem obvious, but these tend to be more faithful to the source than any other speaker I've owned.
-- Jim
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Nearly 2 years now of listening to my Paramount 1.0 300b with 6CG7 mod. PB did say give it awhile before the major surgery of going to 8 pin tubes. The amps sounded so fine I damn near decided to stay with the 6GC7's. My MQ iron pusher forced me into another purchase for my Paramount 45 build, (EXO-145 Nickel and Dowdy chokes built to match), that I figured I better get the conversion done on the old Girls.
The first amp was a royal b!#ch. In detaching the boards and the physical stress rewiring and/or moving wires, I managed to break a wire inside the insulation. Then in testing/diagnosing, managed to short and blow an LED! :-(. Found the issue running continuity checks on all of the wires. So pretty much replaced most of the wires, the 220 ohm grid stoppers and, of course, the sockets. (I bought some Teflon Loktal sockets from the UK, nasty itsy bitsy wiring eyes! Definitely made it far more challenging!) The second amp was a breeze! Go figger!
Threw in a pair of 1943 Philco 7N7's. Pulled my Paramour II 45's, (which never fail to please!), and put the Paramount's back into the system...
Wow! The improvement was not subtle and that was streaming our local Jazz station via Touch. I won't go into all of the flowery verbosity. For right now let's just say everything is better, sweeter, more real. I need to listen more seriously and spin some of my warhorse vinyl and tapes. But for now, my impression is that this exercise was well worth the effort.
A big thanks to the PJ and PB for their patience and support. Special kudos to PB for figuring the driver board changes required. I could never have pulled this off with out the extra effort of these wizards! Now to try to wipe the grin off of my face before bed!!
I'll listen for a couple of weeks or so than close this odyssey.
Cheers,
Geary
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I'll listen for a couple of weeks or so then close this odyssey.
Short and sweet. Changing to the 8 pin Loctal 7N7 from 9 pin Noval tubes is the single biggest improvement in all of the incessant tweaking that I have done to these amps. Both ends of the sonic spectrum were increased and improved. It was literally like I had EQ'd to extend the bass and treble. I spent a great deal of time sorting the treble response on my EV Sentry IV-A's, with abundant mentoring by a life long EV engineer. This tube switch made another quantum improvement in the tweeter's response.
All of the typical audiophile subjective performance categories got a Big A+. Better timbre, imaging and sound-stage. Vocals are simply scary in their palpable presence. The leading edges of transients are shockingly realistic.
Would I have gotten the same reward, for the effort, with Octal 6SN7's? Probably, but, IMO, only with the big bucks, close to unobtainable selections. The Loktal 7N7's, with the highly desirable construction variations, are dirt cheap in comparison!! (I will repeat my long term bias here, I have always found the Octal/Loctal equivalent to Novals to be much more to my taste! Crack, Foreplay EXT. Of course YMMV!) One caveat, I use a line stage, (Smash w/UP). If you are not running a line stage/preamp, you may find the loss of input sensitivity a problem.
PB made a suggestion early in this process and I now wholeheartedly concur, do the soft start upgrade first. Get the amps running as v1.1. It greatly simplifies the process. Listen to the 9 pin tubes of your choice, then take a leap of faith and try the 6SN7 or 7N7. (You can cheat and try a 6SN7 adapter, but I have never been a fan!) The Paramount chassis already will accommodate the Octal/Loctal bases, (just remove the adapter plate!). Thank you PJ for the prescience!!! You can always go back!!!
Now time to build my Paramount 1.1 45's!!! Wanna guess the driver tubes? ;=)
Cheers,
Geary
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One step closer my friend. When you get that itch again, buy a couple of 7n7, 6SN7 converters and shoot me a PM. I'll send you a few pair of 6SN7's to try out. The differences between brands is not small and may yet improve on what greatness you have already achieved.
My next experiment is a 6J5 for the shunt reg side and a 2C22 for the gain stage. I've got a feeling that the tungsol round plates I'm already using will still top it but it's worth experimenting with :)
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One step closer my friend. When you get that itch again, buy a couple of 7n7, 6SN7 converters and shoot me a PM. I'll send you a few pair of 6SN7's to try out. The differences between brands is not small and may yet improve on what greatness you have already achieved.
My next experiment is a 6J5 for the shunt reg side and a 2C22 for the gain stage. I've got a feeling that the tungsol round plates I'm already using will still top it but it's worth experimenting with :)
Thanks Aaron!! Gotta get the Paramount v1.1 45 build done first! There are so many really great 6SN7 iterations available. I ran Golden Tube Audio SE40's for years. They are PSE 6L6GC amps with 6SN7 drivers. Changes in the driver 6SN7's were not subtle!!
I really like 6J5's. I rebuilt an early Foreplay with them. IMHO, it was pretty damn nice sounding!! I am not familiar with the 2C22. The top contacts on the 2C22 might present granddaughter & cat problems!!!
Once the new Paramount 45's are built, I will probably rebuild the Paramount 300B's as V1.1 with TFA 2004 Jr. nickel pinstripe OPT's, PS choke and Dowdy plate choke. The choke selections will really depends on how I like the sound of the Paramount 45's with the huge iron!!
I keep telling myself that will be the end of my power amp odyssey. I kid myself too much!! ::)
Cheers,
Geary
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Hi all. I just completed the swap to 6sn7 drivers on v1.1 Paramounts with the soft-start board. I get a strange resistance reading on B2 (previously B4) of 279K ohms versus 130K. On start-up, I get 355v on B5 (previously B6), and the two LEDs on the left side of the board (those further away from the trim pot) are dim. I double checked wiring and everything is correct according to my translations, but I missed a re-solder on U18, which I've corrected.
I must have fried something on the board. I didn't get smoke, or smell, but heard a very slight sizzle which, at the time, I thought was some loose hardware or wire clippings sliding as I tilted the plate to flip the power switch. Anyway, thoughts on troubleshooting?
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Voltages would tell us a lot, especially those on 6SN7 pins 1-2-3-4-5-6. You may have to unscrew the C4S board and tilt it out of the way. If you can, photos or the socket and both sides of the board would also help. Does the 6SN7 heater glow?
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I will take more measurements this weekend Paul. While not all things are equal since the swap, the manual suggested shutting down immediately if voltages on B5 where above 350vdc. So that's what I did after running for about 60 seconds. Then I went back to check resistances. I'll take photos, and hopefully get them posted to this string.
Chris
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355v is close enough to 350v. This is the voltage set by the Zener string, before the regulator circuit kicks in. There are 5 Zener diodes, 68v each, for 340v. The diodes are said to be +/-5%, so 324 to 357 would indicate they are functioning correctly.
The regulated voltage will be about 300v, so if you still have 355v after 60 seconds, the regulator is probably not working. Tube pin voltages will help figure out why that is the case.
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PJ,
Thanks for being so supportive of the 6SN7 driver conversion!!! I love mine, (7N7) and, to my ears, it is really worth the extra effort!!!
Cheers,
Geary
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It was a steady 355v for that brief period, but I'll watch more closely tonight and report back. I'll echo Geary and say thanks for supporting me with this customization. I know I'm outside the fence a bit.
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Start-up voltage does not decrease, but climbs slowly. Heaters do not glow. LEDs don't light. Voltages are as follows:
B1: 350v
B2: 350v
B3: 0v
B4: 0v
B5:350v
B6: 0v
Not sure if I did this correctly, but I've tried to attach my photos and the pinout translation table.
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The pin numbering appears to be incorrect.
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Pin numbering is incorrect in the translation table, the top-plate, or the wiring? The top plate was labeled during the original build, prior to the soft-start install, and doesn't describe the current wiring.
It might be a little hard to see in the slightly blurry photo, but the keyhole is shown, splitting the difference between the standoffs, and pin 1 is to the lower right with the 220ohm resistor going to L20. Sequence goes counter clockwise from there.
If my translation table is incorrect, then there ya go.
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Pins are numbered clockwise as seen from the bottom. The 220 ohm resistor in the picture is soldered to pin 8, not pin 1. I assume the heater does not glow, because it appears the heater wires are soldered to pins 1 and 2, not to 7 and 8.
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Wow. I'm embarrassed. Sorry for the bonehead error, and for consuming your time needlessly. I'll correct and report back. Hopefully I didn't do permanent damage to the board.
I will say that the PCB that came with the tube socket mislead me. Not sure why it would be labeled as it is. Lesson learned.
Chris
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I just worked on an amp with a nine pin aftermarket socket that was numbered like that as well. It's useless unless it is marked top and bottom.
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It sure is useless. I've used 9 and 4 pin versions of these sockets, with and without the PCB, and haven't had this problem before. It's my bad though. Hopefully this string will keep others from making a similar mistake.
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Well, permanent damage has been done. No voltage on B1-B6, and no LEDs light. Filaments on 300B glow, but that's the only sign of life.
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Well, permanent damage has been done. No voltage on B1-B6, and no LEDs light. Filaments on 300B glow, but that's the only sign of life.
No....permanent repairable damage has been done! Hang in there!!!
Cheers,
Geary
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Right. True. No obvious signs of trauma on the board, so imagine it's one of the transistors.
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Do you at least get a glow from the driver tube?
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I do actually. I couldn't see before with the unit flipped over, but confirm the driver glows.
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Okay. Back in business. Resistance checks are good. Voltage checks are good. LEDs all light. Trim pot set to 175v.