Bottlehead Forum
Bottlehead Kits => Legacy Kit Products => Topic started by: Grainger49 on January 01, 2012, 11:15:51 AM
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I'm going to make some changes to my Paramours. They are one of the last four pair Doc put on sale just before the Paramour II came out. So mine are very late production.
Today I got a little aggravated at myself because I hadn't adjusted the hum pot since changing tubes. The belly of the beast is filled with stuff I added making it dangerous to adjust anything. Today I put the hum pot shafts through the top plate. I wish I had heard of this before assembly, there is the perfect place on the top plate in front of the power transformer and back from the input jack.
I'm happy with this, I got one amp to 1mV hum, the other to 1.8mV. The sub woofer's plate amp has some physical vibration that hums louder than the system now.
More later, less sooner.
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Excellent! And now you know why the hum pot is on top of the chassis in the Paramour II. (You've probably already figured out why there's an IEC socket... :^)
Before the Paramour, and before we got into parafeed, I made a 2A3/300B amp based on the original SEX monoblocks. Must have been around 1997, documented in VALVE under the title "S.E.X. and the Single 300B" - Grainger, I'm sure you remember Helen Gurley Brown! It was the same chassis plate that was used for the first Paramour, and that's exactly the same place that I put the hum pot, for exactly the same reason.
It ran a little hot, about 18 watts, which is why we had a custom power transformer made for the Paramour. I had a bunch of cheap Shuguang biplate 2A3s; back then they had a habit of crapping out before they hit 1000 hours irrespective of the plate dissipation, so I thought "smoke 'em if you got 'em" ... that amp served me well for at least a decade. :^)
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Ha, ha! Paula asked, "What?" when she heard me laughing over here. I remember Sex And The Single Girl, but never read it. Maybe I should have? I needed a lot of pointers in those days. I never got them either.
The lack of an IEC socket hasn't bothered me too much, just some breaking solder joints. I feed more of the power cord into the base then flip and work on it. I haven't found an IEC power cord long enough to reach neatly from my right amp to my P300. If I put on an IEC it will be on the back of the base then I will mount the toroidal balun to the base and run stranded all the way to the power input terminal strip. The solid wire broke from the balun to the terminal strip on both amps when I worked on them yesterday.
I have a short list of "upgrades" for these and will update the thread as I go. Soon I will put a picture in of yesterday's work.
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PJ, elsewhere in a thread started by xcortes, has suggested a shorting switch to short the primary (after the Parafeed cap) of the output transformer. I think the reasoning is that the startup bleeds some DC through the Parafeed cap and magnetizes the primary of the transformer. It takes half to an hour to clear it out and the amp to sound its best.
I mistakenly bought a pair of DPDT toggle switches with a spring return to center off from one position. I can use these! Thank goodness I'm a pack rat and didn't throw them out. I will turn on the amp, hold the switch shorting the primary for 30-60 seconds then turn on the other amp.
Edit: I must have discarded the switches or lost them. I used a SPST switch on each amp. There was no smoke but I have to turn the switches off. I won't forget because I'm going to be kneeling in front of the amps to turn them on anyway.
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So when I changed the drivers tubes to 76s I got help from PJ with setting them up. I got the plates to 250V and since he said +/-50V from 200V, the target, I left them there. Then working with Paully on his next project I found I am running them pretty hot. Maybe that is why I eat up driver tubes and not output tubes.
A little calculating and a quick search through my resistor collection, I paralleled a resistor with each cathode resistor. Now the combination measures 1988 ohms, each, and the voltage is 197V. Much closer to target!
Next a bypass of the cathode cap or a replacement for it. (probably a bypass)
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If I had looked I would have seen that the cathode bypass cap is already bypassed. One of the olides, like me, had used a 10 turn pot for the hum balance pot in his Paramours. I got the number from him, I think ElCraigo, and put them in the other day.
I have made several tube changes, not because they were worn, just because, and I got the hum tweaked 5mV and 7mV lower than I could with the lower resolution stock pots.
This is a great move. I waited 20 minutes after starting to listen to do the final trim. Should have rechecked at the end of the listening session but didn't.
I had also wired one of the "primary shorting switches" improperly. (reply #3 above) My Paramours are a mess inside and it took 4 or 5 comparisons to see my mistake. I am now shorting the transformers at startup every time, shut down too just in case.
I still go through ear warmup but I am certain that the transformers are not molested on startup.
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Grainger, Could you walk me thru setting the hum pot on Paramore. I just do it by ear, Is there another way?
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I use the meter method, others listen. But you can reach a lower hum if you use the meter.
Short the inputs, I use a pair of alligator clip jumpers, one for each channel. Attach your meter to the speaker leads. I put the meter leads through the holes in the 5 way binding posts and tighten the plastic part down on them. This is a hands free method to read the magnitude of the hum voltage.
Set your meter to AC volts, the lowest range if it has ranges. Turn on the amplifier and let it warm up for 15 minutes. If you are just measuring hum, this is what you have. Posting be sure to include the milli-volts (mV) reading.
Start moving the hum balance pot one direction. If the voltage goes up change directions. When you get it to lower find where it begins to climb again while moving in the same direction. You have just passed the null point. Now very carefully make minor adjustments to the pot to get the lowest number, milli-volts, you can on the meter. It is best if you use a 4 digit digital meter. This gives you the greatest accuracy.
The stock pot is wire wound and the limit of resolution is "one knuckle." That means one wrap to the next wrap of wire. They are good pots but don't have the resolution that a 10 turn pot has. The half way point between knuckles shorts two windings together. This is why I went to the 10 turn pots for my Paramours in the hum balance circuit.
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For what it's worth, we now "sandwich" a 10-ohm pot between two 22 ohm resistors, giving 5 times as much resolution.
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Thanks for the info both of you. One question is it all right to play the amp w/o speaker hooked up? I have not done it thinking I would damage things.
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Yes, I do it whenever I swap the speaker leads for adjusting absolute phase. These are no feedback amps. They are fine without the load on the secondary of the output transformer. My Stereo 70 is NOT!
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I'm wondering.... Now that I can afford it....
What if I put a film cap on my cathodes. The stock cap is 220uF, haven't looked at the voltage.
I'm looking for large value film caps and I have found a 100uF@400V Obbligato film power supply cap. I am hoping not to need two of these.
What is the effect of lowering the value of the cathode bypass but increasing the quality?
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Grainger,
Consider using a couple of the Icar caps I used in the power supply of my Crack. Check the links at the bottom of the (very long) first post in this thread (http://www.bottlehead.com/smf/index.php/topic,4775.0.html). At only $10 each, it is a much more economical solution, and I have been extremely happy with how well they worked in my Crack. They are available in both 200uf and 250uf (not to mention 300uf) versions.
Regards,
Adam
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Hi Grainger,
I've put 100's (film)on the 45 amp and on a 2A3 amp I have. I went as low as some 51Uf Axom caps. I gave it a 2 week listening period and changed back to the 220. Seemed to lose some of the bass definition, some of the classical music I listen to wasn't as clear or as deep (these were the only things changed in the systems). Now I'm on 350 JJ's electrolytics, these are just in the break in period but it doesn't sound worse. I went away from film due to size considerations and I think a film would be wasted here (maybe a bypass, I've got some 3.3 Solen's I can put in). Is it critical for a film here? I was thinking of going up to around 470uf to see how it sounds. Please post the results of you Obbligato experiment.
Alonzo
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Adam,
I'm going to have to consider the ICAR caps. They will have to stick out the back of my bases like a... I can't come up with an analogy.
Did you link a source for them?
Alonzo,
You have convinced me that the value is critical. The above linked ICAR might be just the thing for both of us!
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Fortunately, you don't have to come up with an analogy. Just use mine:
"Adding insult to injury, the Crack was force-fed a steady diet of meat and potatoes, until the Crack's ass swelled to enormous proportions --- there was no sign of its lithe and shapely body from earlier days. While a goose's liver will turn into foie gras, this Crack clearly had too much junk in the trunk...two cancerous blue tumors sprouted off the rear of the Crack. ... Just keeping those enormous butt-cheeks in place required the Crack to don a girdle before venturing into public..."
Here (http://www.ebay.com/itm/230968898220?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649) is the eBay link.
Best regards,
Adam
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Bought!
BTW, I'm going to copy the analogy and send it to my wife.
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Well, Grainger, it was nice knowing you. But there are probably less painful ways to commit Hara-kiri.
Doc, I think you can close Grainger's Corner now.
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Ha, or he will use his current surplus of money on some pressure tested carbon...
Grainger, at last count there are 17 caps under the hood of my 45 amp. I've got Blumenstien cases so no outboards or girdles allowed.
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"I've got Blumenstien cases so no outboards or girdles allowed."
LOL...too funny!
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The caps arrived a few minutes ago. Maybe I should have read the dimensions?
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi244.photobucket.com%2Falbums%2Fgg7%2FGrainger49%2FBottlehead%2520Equipment%2FDSC02718_zpse0bf1d6a.jpg&hash=af8cea442564d0a50321b047c344548c90d81d81)
Only one cap will go in each Paramour. But there is no room under the hood. These are the largest caps I have for the Paramours. I'm going to have to figure something out. Even if I drill a BIG hole in the back I'll need something to mount and support the caps. They would tip the Paramours backward without something under them.
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Wow, those are big. Glad I didn't take the bait and get them, imagine me shoving them in here...
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Alonzo,
That is full of caps. Is it the Paramour II footprint? The Paramour (one) is the size of a FP 2 or Seduction. So I already have it full with 10uF Obbligato film/oil Parafeed caps (with KK Teflon 0.1uF@600V bypass), film and oil power supply caps and KK Teflon 0.1uF@500V interstage caps. The cathode bypass caps are the only ones that haven't been replaced. This thread, one post, shows it:
Paramour Blivit (http://www.bottlehead.com/smf/index.php/topic,1185.msg8364.html#msg8364) [dead link]
You guys know what a capacitor junkie I am but these have stunned me. When Paula got home last night I showed her the caps they are replacing, I have some in my stash, and then the replacements.
She agreed, I would have to support under the caps to keep them from tipping the amps over.
The voltage on it isn't too high so I will just use stranded wire to connect it to the cathode resistor and leave it behind the amp.
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Grainger,
It's a Stereomour box, CLCRC with 100Uf/100Uf/70Uf for the power supply. The last 100 is bypassed with the 10Uf Obbligato film/oils above the 70Uf's. The parafeed caps are 10Uf Obbligato golds, the cathode bypasses are 350Uf Jensens, 15Uf Solen's across the 45's heater pins, 3.3 Uf Obbligatos on the grid chokes and a 0.1Uf on the PS input. I think that's all of them, there may be some buried under stuff that I forgot. Way too much overkill in caps' but I had them so why not use them.
Let us know how those 200's sound.
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If you got 'em smoke... No that isn't a good idea, USE them!
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If you got 'em smoke... No that isn't a good idea, USE them!
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Grainger, you have to get rid of the green! It's invisible quotes.
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I hope that is better. I edited this thread on break at work today. I hadn't realized that I greened a quote.
It is ok for posts, isn't it? It looks good on my two computers at home and at work.
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The caps arrived a few minutes ago. Maybe I should have read the dimensions?
Only one cap will go in each Paramour. But there is no room under the hood. These are the largest caps I have for the Paramours. I'm going to have to figure something out. Even if I drill a BIG hole in the back I'll need something to mount and support the caps. They would tip the Paramours backward without something under them.
Have you ever try a capacitance multiplier? I've used them in low level applications, but I haven't tried them at power.
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Have you ever try a capacitance multiplier? I've used them in low level applications, but I haven't tried them at power.
VS, it's way back at the beginning of this long thread, but the application is a bypass capacitor on the 2A3 cathode bias resistor. I can't see how a cap multiplier would work there. Unless you have something new? It wouldn't be the first time!
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Have you tried the cathode mod?
http://www.siteswithstyle.com/Voltsecond/Paramour_cathode_mod/Paramour_cathode_mod.html (http://www.siteswithstyle.com/Voltsecond/Paramour_cathode_mod/Paramour_cathode_mod.html)
With the speaker ground attached to Single Point Ground (SPG), 60V on varnished magnet wire inside a transformer is fine.
-Corona doesn't start until ~205V peak ( JPL D-8208 ) at 20kHz at room pressure. However, I wouldn't trust 60V on magnet wire used for point to point wiring because of the higher amount of abrasion on the enamel from handling.
-Should Murphy cause a short, the wire to SPG keeps anyone from being shocked. Output rtn to SPG is even a point where I would use Ying-Yang diodes if I needed to break a ground loop.
You may want to also play with a power on delay.
http://www.siteswithstyle.com/Voltsecond/B+_Paramour_delay/Paramour_delay.html (http://www.siteswithstyle.com/Voltsecond/B+_Paramour_delay/Paramour_delay.html)
Using a capacitive multiplier on the cathode, sounds like an OUCH project that could be fun!
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V-S, Yes, I returned the OPT to the top of the cathode resistor/capacitor when I upgraded to MQ Iron.
Does this make a better Cathode bypass cap irrelevant?
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Does this make a better Cathode bypass cap irrelevant?
"Irrelevant" is too strong of a word. If it sounds better, do it.
My concerns is that a physically large cathode bypass cap can cause coupling to adjacent parts that could be hard to fix.
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Check the picture in reply #20 on the second page. I think those would have to sit outboard to the base. There is no room under the hood to put much of anything.
There are no children to worry about, you know my age.
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Because of the finite inductance of the plate choke, you do get deeper bass with the bypass cap in place. It may make more difference in theory than in practice (most of the effect is below 40Hz) so try it and see, as VS says!
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The cathode cap also helps flatten the frequency response in the presence of parasitic capacitance (Transformer primary to Secondary)
Externally mounted with twisted wires from the cap to inside should solve any coupling problems.
Insulate the leads on that external cap, I know adults that can't resist touching every thing or who can't point at something (instead of touching it) and say "What's that do?"
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. . . Insulate the leads on that external cap, I know adults that can't resist touching every thing or who can't point at something (instead of touching it) and say "What's that do?"
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi244.photobucket.com%2Falbums%2Fgg7%2FGrainger49%2FSmiles%2FROLF.gif&hash=d8c25de5059c9863b539eef0d5a5f9c5fb975e51) . . . (https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi244.photobucket.com%2Falbums%2Fgg7%2FGrainger49%2FSmiles%2FROLF.gif&hash=d8c25de5059c9863b539eef0d5a5f9c5fb975e51) . . . (https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi244.photobucket.com%2Falbums%2Fgg7%2FGrainger49%2FSmiles%2FROLF.gif&hash=d8c25de5059c9863b539eef0d5a5f9c5fb975e51) . . .
I was fine till the last sentence. Then I thought of way, way too many people I know. Most are afraid of touching my stereo, but then....
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Grainger how are those Icar 200uf's working out?
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They are still sitting on my shelf. I intend to wire them in with long wires coming out the back of the amps. I just have been working in the yard so much I spend all audio time listening rather than tinkering.
I will report back.