First, I am envious of your repair skills though not of the problem you face.
In the absence of any similar ability on my part, were I in a similar situation, I'd definitely be trying to contact Mike Sanders at Quicksilver to see what help he might provide. Apologies if this obvious course of action has already occurred to you and been rejected for some reason.
info@quicksilveraudio.com
Good luck finding a fix.
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Its a bad tube or its really sick.
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Thanks ghosthouse, i guess i will be contacting quicksilver. I will need to take a detailed pic of the unit and detail all of the components i have changed out.
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Have you double checked for a cold solder joint, especially at the left channel tube/s sockets?
How good is the tube pin to tube socket contact connection? Is there good friction resistance contact holding pressure when plugging a tube in as well as when pulling a tube out? Poor contact pressure can cause the noise you are hearing.
The old tubes that you replaced. Was there any evidence on the pins of the tube\s that any contact enhancer was used? Hopefully not... If the pins showed any evidence an enhancer was used you may have dirty tube socket contacts. Dirty and or corroded tube pin to tube socket connections can cause the sound your are hearing.
Have you ruled out any chance the left channel of the power amp was damaged when the preamp tube shorted? Did you try reversing the interconnects from the preamp to power amp at the power amp's input jacks to see if the noise then moved to the right channel?
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In tube gear a blown tube often doesn't 'die peacefully' and it may 'take away' more circuit components such as resistors and DC capacitors .
It's not hard to repair, but probably techies will charge arm/leg + shipping.
Enjoy the tubes.
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Hope Mike doesn't get too upset about the changed parts! Some engineers do, Frank Van Alstine and Mike's buddy Roger Modjeski being two such. |
Oh my you are right on builders getting upset. Sounds like a resistor to me and did you look very closely at them? |
Lost my left channel recently in my Quicksilver preamp( full function ). It was a resistor. My tech said the value of said resistor was being run to operational maximum and sub'd in a higher value. I tried putting in a couple Takman Rey which were closer to original value to see if I could hear a difference and I got random loud popping although it did sound better. |
Everyone thanks for the suggestions! I have 7 more resistors to replace and then I will have replaced all resistors. I will replace those in the next week or two and then the socket on that channel. The thing that gets me is that I have already replaced all resistors that exist in pairs. I would have thought that with one channel having the issue that the damaged component would have been a component that existed in a pair. This leads me to believe it is in the socket, though there are also two relays. Oh well in the end I will replace everything, and I am sure the very last thing I replace will be the component with the issue. Yeah I was also kinda worried about the whole premadonna engineer issue, that will not fly with me, I am also an engineer, but I am a plant electrical engineer, not small circuit stuff, 480 at lots of amps, big motors encoders, solenoids, starters, relays and such. To me components meet/exceed spec or don't, I don't have much time for whiny engineers, I deal with enough of them professionally.
Please keep any suggestions coming and thanks again! |
LOL " I don't have much time for whiny engineers, I deal with enough of them professionally"
True Dat :-) |
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I have 7 more resistors to replace and then I will have replaced all resistors.
How do you know they're bad? Do(Did) you see signs of burning? Trim pots must also be checked. Do visual on DC caps if they changed shape or leaking. |
Czarivey, I dont know if they are bad? Because i dont have a schematic i have to remove each resistor and test then cross refrence as they are 6 band precision type. I wish i had a tracker tester. I then order the same value 1% at highest dissipation usually 1 to 2 watt depending on availability. There are no trim pots, all electrolytics have been replaced except 1 and its on order (but it visually looks good). |
Quicksilver on older preamps may have schematics... check with manufacturer or even hifiengine.
Auto-bias circuit and proper bias needs to be measured on faulty channel. I've seen Quicksilver would use Zenner diodes (some semiconductors in the mix) to provide auto-bias to tubes. Zenner diodes can go bad within time. I'm not sure if your preamp uses such. You also need to measure all output voltages for the faulty channel out of power supply. Start from B+ and compare it to healthy channel. It clearly seems to me that you don't have the right offset quiescent voltage supplied to the faulty channel tube making an amp to oscillate on low frequencies.
If you DIY savvy, you should look for vintage units that have schematics.
There are plenty of very well built tube units done in 50's...70's with schematics -- just my $.02
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Czarivey, thanks for the advice! Have done a limited search for schematic snd found none. I did replace diodes even though they tested good on my meter. If its not the the remaining resistors maybe its the damn socket itself, but resistance wise it measues like the good channel.
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I would ask Mike(Quicksilver) to share schematics of ANY full function preamp they've ever built. You may find lots of similarities to your unit.
Also check conducting 'trails' over PCB around blown tube making sure that there's a continuity of applied voltages. Re-apply and/or retouch solder on entire board making sure that you don't have loose joints. I often go over with magnifying glass and find LOTS of cold or loose joints as a matter of fact especially in tube equipment.
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