Bottlehead Forum
Bottlehead Kits => Legacy Kit Products => Topic started by: patrickamory on November 11, 2018, 04:58:24 AM
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So I continue to enjoy my revived Paramour 1s, but the hum is significant through my horns. Implementing PJ's recommended C4S ground connection from B9 to T14 did not have any effect on it.
Ancient components and clumsy soldering: I decided to reflow all the joints on one unit to see if that helped.
After doing that, the lowest I could get the hum was 27 mv, which is about 10X what it should be. This is with a shorting plug in the input jack, the amp warmed up for 15 minutes, and measuring VAC across the speaker terminals.
What should I attack next? I have located replacement filter caps, cathode bypass caps, grid blocking resistors, coupling caps, parafeed caps, binding posts, etc. in my workbench or online. Are any or all of these likely to be the culprits?
I also have extra ceramic 9-pin tube sockets. I don't have any extra bakelite 4-pin sockets, and in fact a small piece of one of those cracked when I inserted the new Sophia Electric 2.5V 300B in it a couple weeks ago.
Or... is it likely to a problem with PTs?
Thanks for any advice you guys can provide. Still loving the sound of these, just would like to get that noise down.
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Out of curiosity, where are you located?
Do your power transformers say "PT-2" or "Hammond" on them?
Can you post some photos of your build?
Is your noise 60Hz or 120Hz (listen to these tones online, then let us know which noise sounds more like what's coming out of your amp).
I would very strongly suggest not just replacing random parts. There's something else at work here that needs to be diagnosed and debugged first.
-PB
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Located in New York City (Manhattan).
Power transformers have the Hammond "H" on the side sticker and say Made In Canada. I'm pretty sure my kits were among the first round of Paramours and that this is the original PT.
Photos at these links - these are the same that you helped me with in the thread "Paramour 1 with various upgrades" two below this one - except that I have fixed a couple of the issues that you noted, as discussed there:
https://bottlehead.com/smf/index.php?action=dlattach;topic=11132.0;attach=16577
https://bottlehead.com/smf/index.php?action=dlattach;topic=11132.0;attach=16579;image
https://bottlehead.com/smf/index.php?action=dlattach;topic=11132.0;attach=16581;image
https://bottlehead.com/smf/index.php?action=dlattach;topic=11132.0;attach=16583;image
I think the noise is 120 Hz, having compared the sound to a couple of YouTube videos.
Thanks,
Patrick
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If the DC voltages are correct and you have 120Hz noise, I would be looking at how well connected your power supply caps are.
I see some "extra" ceramic caps in your amps, they are not anything we ever prescribed.
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Ah those ceramic caps... I have a vague recollection of a VoltSecond or Quest noise reduction mod for the C4S Paramour. Some kind of snubber, and ceramics were recommended.
Should I remove them?
Is it worth replacing the 220uf 47uf electrolytics at the same time?
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Yes, I would remove the caps, especially since you have the C7X in the power supply.
What is the voltage rating of those 220uF caps? I believe 47uF/450V parts were supplied originally.
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Sorry I meant 47uf!
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The caps are old enough that it won't hurt to replace them.
I would recommend the Panasonic ED radial caps with leads. These are a lot easier to install than the old snap-in caps.
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Removed the ceramics in one unit. Voltages all check out.
But the hum is still 29 mVAC if I'm reading the meter right - please see attached photo. I hear the buzzing now as a little softer and more trebly when hooked up to the speaker, compared to the unit that still has the mod in it.
Next step: order the Panasonics and replace the 47ufs?
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On your meter, there is the "mV" setting that will more accurately display the reading, but I'm sure it will be about the same.
The hum pots are working properly also, yes? (Just to tackle the obvious)
I'd go ahead and replace the power supply caps. I'd also recommend ordering a pair of 220uF/250V Panasonic ED radials to replace the cathode bypass caps while you're in there.
These efforts may not resolve the buzz, but it will remove something from the list of possibilities.
-PB
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Yes the hum pot seems to be working - the figure varies from about 40 down to about 27 mV.
I'll replace the PS and cathode bypass caps and report back after.
Thanks again,
Patrick
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One thought, when you adjust the hum pot, is the lowest reading you get somewhere in the range of adjustment. Meaning not at one stop or the other...John
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One thought, when you adjust the hum pot, is the lowest reading you get somewhere in the range of adjustment. Meaning not at one stop or the other...John
Hi John yes... more or less in the middle I think. Patrick
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I'm now in the process of replacing the PS capacitors, and I suddenly noticed from the original Paramour instructions and diagram that I don't have the 270 ohm WW resistor connecting terminals 5 and 15 - in either amp.
I'm not sure how I lost this, but could its absence be the source of my extremely high hum level?
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You have a 270 Ohm 10H choke in that position instead.
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Oh right - I completely spaced on that :)
So I have installed the new caps and am reading -2VDC at terminal 5 and 15. Resistance check shows open at terminals 1, 2 and 4.
Did I fry the diodes?
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You'll have to be a bit more generic with your voltage values; I have no idea where my Paramour 1 manual is at the moment and I don't have an electronic copy.
If you have -2V coming out of the positive side of your rectifiers, then there's a problem (blown fuse?). As always, posting photos can be helpful.
-PB
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Hi Paul -
Sorry for the vagueness.
The fuse is intact.
Attached are photos of the voltage readings page of the manual, and a photo of terminal strip 1-5. I did move one of the diodes from the top to the bottom hole of terminal 5 because it was getting a bit crowded on top.
Thanks,
Patrick
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If a diode body shorts the two terminals where the capacitor connects, you will get no voltage out of the rectifier bridge or full wave rectifier and you will damage your power transformer (though the fuse should pop first).
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So it sounds like I have an open connection somewhere... will check tomorrow, thanks Paul.
Patrick
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No, I think you have a short between two adjacent terminals. It looks like those two terminals where that capacitor is in your photo are connected together.
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Hi Paul -
I don't think so? Please see more detailed photos attached.
I read increasing and decreasing megaohms between the two terminals which I'm assuming is the effect of the capacitor.
Please let me know what I'm missing...
Thanks,
Patrick
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That last angle does show separation.
You can measure the AC voltage between brown and purple to ensure that the power transformer is still delivering the goods.
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Hi Paul,
I measure 642VAC across brown and purple. So the PT is alive?
I should have mentioned that both tubes glow, and the C4S diodes light up.
Thanks again,
Patrick
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the C4S diodes light up.
Then your high voltage DC rail is operational.
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Thanks Paul - I just measured VDC at 5 and 15 now and they are fine.
Hooked up the amp and the hum is almost inaudible (the gain is slightly less too - but only slightly actually the gain is much lower).
So on to the next unit now - hopefully replacing the filter caps has solved the problem! Thank you once again for all the help.
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Now I've done the other amp, voltages all check out correct, but I'm getting a tiny, distorted signal.
I did replace the binding posts - I'm guessing there's a poor connection there if all voltages are on point? Will try reheating tomorrow.
Getting there.
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Second amp is putting out a very low, distorted signal. I read 0.19 VAC on a 60 Hz test tone, input jack shorted. I switched both tubes - same result. Voltages all check out as do resistance readings.
Solder joints for the 3 replaced caps all seem fine.
Any suggestions on what to check next?
(The good news is that the hum is down to 2.6 mV.)
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You can play the 60Hz test tone, then measure the AC voltage at the RCA jack, at pin 3 of the 4 pin socket, and at the speaker binding posts, then report those readings here.
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Hi Paul,
Here are the readings at those points with the 60 Hertz test tone, plus T25 (where the positive end of the parafeed cap connects to the blue wire from the OPT):
- RCA jack: 0.03 VAC
- A3: 11-13 VAC
- Binding posts: 0.08-0.10 VAC
- T25: 17 VAC
Thanks again,
Patrick
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There is something connected on the primary of the OT or on the output of the OT (including the binding posts) that shouldn't be there or that is touching both terminals. The signal is sitting there appropriately on the input side of the transformer but isn't making it out. There should be a little less than 1V of signal at the binding posts under your testing conditions.
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Hi Paul,
I'm stumped. I can't see any short circuits or connections in the area. Is it possible there's something wrong with the OPT?
I've attached some pictures.
Thanks,
Patrick
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Sorry to say but a lot of the solder joints don't look good at all, especially the strip adjacent to the outputs. If it were me I would cut/unsolder all of them and start over...John
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Sorry to say but a lot of the solder joints don't look good at all, especially the strip adjacent to the outputs. If it were me I would cut/unsolder all of them and start over...John
No worries about criticizing the joints - I made this amp 17 years ago and it was my first project... they are really ugly, I agree.
I'll give that a try and see if it solves the problem. Thanks!
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Well, I reheated and cleaned up the solder joints on the terminal strip by the outputs.
Reconnected the amp, and now it doesn't power up at all! Which is odd because I didn't touch the PS.
Checked the fuse - intact.
Power cord wiring - intact.
Power supply wiring and joints - look fine.
Checked resistances - all check out except for T25 which should be 200 ohms but is coming up at 1200 ohms - I don't know if this is significant? T25 is where the positive side of the parafeed cap connects with the blue lead on the OPT, which the documentation says connects the primary to the plate.
Checked voltages - 120 VAC from the power cord, 0 VAC at T1 and T2, other side of the PT.
Any further advice?
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Based on your descriptions during this thread, every time you are going in to do work on the amp, the problems it has change. This does indicate lots and lots of flaky solder joints. Starting over isn't a bad idea, and if you sent it to me for legacy kit repair work, that is likely what I would do.
-PB
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Based on your descriptions during this thread, every time you are going in to do work on the amp, the problems it has change. This does indicate lots and lots of flaky solder joints. Starting over isn't a bad idea, and if you sent it to me for legacy kit repair work, that is likely what I would do.
-PB
I think the PB's advice is spot on! It is a simple build with relatively few solder joints. Disassemble, lose the stranded wire and re-solder all of the connections with good solid core wire. You will likely spend more time chasing problems around the unit than a rebuild would take.
Cheers,
Geary
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Thanks guys! I'm going to do it.
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I have not replaced the wiring but I have resoldered every component and am still seeing the same problem and getting the same voltage readings.
Before I send this off to Paul (if he'll accept it), I wonder whether there's an obvious problem that anyone can see from the input voltages - possibly a problem with the power transformer? The PS voltages are at 60-80% of what they should be. The C4S diodes don't light up (I thought one was bad but it's fine), and zero voltage reaches the 2A3.
I've even disassembled the power cord and checked that 120 VAC is coming through from the wall.
HV secondaries: 262 VAC on each (315)
First filter cap: 250 VDC (395)
Second filter cap: 176 VDC (390)
2A3 filament: 0 VDC (60)
2A3 plate: 0 VDC (365)
C4S input: 122 VDC (295)
12AT7 second section plate: 120 VDC (155)
12AT7 second section cathode: 1.3 VDC (2)
The figures in parentheses are the proper voltages according to the manual & C4S manual.
All resistances check out.
Both tubes glow.
It seems to me that insufficient power is making its way through the PS to the C4S, which in turn means the 12AT7 is not driving the 2A3.
I have checked and resoldered EVERY connection throughout the PS, paying special attention to the PT leads.
Sorry - I promise this is the last post I'll make about this amp if the answer is still bad soldering joints - but I thought that maybe the consistency of the voltage readings might be a clue.
[Edit: attached original schematic, pre-C4S.]
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First filter cap: 250 VDC (395)
Second filter cap: 176 VDC (390)
You are on the verge of destroying this amplifier. That is 275mA of DC current being drawn from a transformer designed to provide 75. You will blow these up if you keep running them.
If the 2A3 plate is 0V, then this is extremely concerning. Perhaps the 2A3 isn't inserted in the socket properly?
Something is drawing way more current than it should. The power transformer voltages seem low because you're slamming it with several times what it's supposed to provide.
You are welcome to send these to me, but I will strip everything out any only reuse the transformers.
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This made me look up my old manual - sure enough, there is no resistance test at the 2A3 plate. We must have thought there was no possible way the plate could be grounded. We were so innocent back then!
Anyhow, the plate IS grounded. No point in checking anything else until that's resolved. Only two components connect to the plate; that should make it easier, right? :^)
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This made me look up my old manual - sure enough, there is no resistance test at the 2A3 plate. We must have thought there was no possible way the plate could be grounded. We were so innocent back then!
Anyhow, the plate IS grounded. No point in checking anything else until that's resolved. Only two components connect to the plate; that should make it easier, right? :^)
PJ you were absolutely right! For some reason I had a lead connecting T21 back to T12, thus grounding the plate. I must have mistakenly soldered that in when redoing the wiring around the cathode bypass cap which I replaced at the beginning of this project.
The diodes light up and all voltages read correctly now.
On to the hum adustment and then putting this back in the system. PB, I will probably send both amps to you for a rebuild anyway when my regular amp returns from the shop. Thank you so much for your help, gentlemen.
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We must have thought there was no possible way the plate could be grounded. We were so innocent back then!
I did see this once in a SEX kit also. It's imperative to check the DCR of the plate choke on that channel to be sure it survived the incident.
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I did see this once in a SEX kit also. It's imperative to check the DCR of the plate choke on that channel to be sure it survived the incident.
Check it out of circuit right? And it should be 270 ohms?
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Yes, you should be able to measure it in circuit. It may be off by 10% or so; that would be normal.
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I get 260.3 ohms, in circuit.