you need to know the actual dissipation first...maybe all that is needed is to lift those resistors far away from pcb surface by at least 12mm..
Working channel is on the left mean perfect, no problem, no bump.
Right channel has bump/thump and burning smell. At first after upgrade the caps, there was a smell but worked fine for over 40 hours except for the bump, so I replaced another cap to see if the bump get away but now it keeps smelling every time I turn on so I turn off right a way.
So after replace the cap, I realized the smell may come from the overheat resistor.
Right channel has bump/thump and burning smell. At first after upgrade the caps, there was a smell but worked fine for over 40 hours except for the bump, so I replaced another cap to see if the bump get away but now it keeps smelling every time I turn on so I turn off right a way.
So after replace the cap, I realized the smell may come from the overheat resistor.
it could be other things, such as pin type connectors getting loose, this is my beef with these amps, contacts can become high resistance and cause a lot of grief, if that amp were mine, i will use direct soldered connections instead..
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what is the dc voltage readings wrt to ground on the cathodes of the 6sn7 cathode followers? are they the same as it should be?
if you can tell me, we can calculate plate current of the 6sn7 cathode followers...
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what is the dc voltage readings wrt to ground on the cathodes of the 6sn7 cathode followers? are they the same as it should be?
if you can tell me, we can calculate plate current of the 6sn7 cathode followers...
O.K. Following Tony's reasoning, you can "isolate" the capacitor desoldering just one pin of R133 and R42, do not forget a new photo, many times capacitors that measured well are failed.
Leaky/overheated electrolytics does smell awful, and sometimes they leak a kind of toxic vapour.
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that is part of it, i hate pin connection on any tube amp, period...
direct soldered connects are still the best for me anyway...
Got its working now after swapped out both resistors last night. The resistor measurement is the same as the left channel now.
Here is the summary of what happen;
1. Everything was working with original parts.
2. Swapped new upgrade coupling caps. First turned on that smell the burning. I thought it was the tubes so swapped the tubes around then no more smell and got it working for a week except for the bump/thump on right channel.
3. Decided to swap a new coupling cap that near those 2 resistors. Then every time turn on, the smelling of burning started again. No matter I tried to swap the tubes as before that didn't work
4. Finally saw a red color mismatch on one of the resistors even thought the resistor was looking good, no sign of blow or anything except a little dark in the middle and red was changed to black. I guess because it's overheated.
5. So far everything is good after testing 2 hours last night.
Here is the summary of what happen;
1. Everything was working with original parts.
2. Swapped new upgrade coupling caps. First turned on that smell the burning. I thought it was the tubes so swapped the tubes around then no more smell and got it working for a week except for the bump/thump on right channel.
3. Decided to swap a new coupling cap that near those 2 resistors. Then every time turn on, the smelling of burning started again. No matter I tried to swap the tubes as before that didn't work
4. Finally saw a red color mismatch on one of the resistors even thought the resistor was looking good, no sign of blow or anything except a little dark in the middle and red was changed to black. I guess because it's overheated.
5. So far everything is good after testing 2 hours last night.
Got its working now after swapped out both resistors last night. The resistor measurement is the same as the left channel now.
Here is the summary of what happen;
1. Everything was working with original parts.
2. Swapped new upgrade coupling caps. First turned on that smell the burning. I thought it was the tubes so swapped the tubes around then no more smell and got it working for a week except for the bump/thump on right channel.
3. Decided to swap a new coupling cap that near those 2 resistors. Then every time turn on, the smelling of burning started again. No matter I tried to swap the tubes as before that didn't work
4. Finally saw a red color mismatch on one of the resistors even thought the resistor was looking good, no sign of blow or anything except a little dark in the middle and red was changed to black. I guess because it's overheated.
5. So far everything is good after testing 2 hours last night.
What about the bump at start-up?
I checked the resistor with LCR-T4 Digital tester so I don't know the voltage after turn on. But so far both are the same as on the left channel.
The bump is still there, very light pop sound but not noticeable as before and pretty much the same as the left channel. Before was like a loud pop but working. Kinda annoy. I guess it's a typical tube amp?
Both channels: No hum from 0-75%, a light hum from 75-100. 40% is good enough to listen so I am not bother to troubleshooting.
The bump is still there, very light pop sound but not noticeable as before and pretty much the same as the left channel. Before was like a loud pop but working. Kinda annoy. I guess it's a typical tube amp?
Both channels: No hum from 0-75%, a light hum from 75-100. 40% is good enough to listen so I am not bother to troubleshooting.
The weird thing was after replaced the upgrade caps, the first turned on was smell. I believed that was the start from there but its working fine except loud bump on right channels where the smell around the upgrade cap. Since the resistors are near that upgrade cap, maybe it was from the resistor instead I thought it was the cap. The smell was gone after swapped the tubes so it's hard to troubleshooting.
I've been wondering how you knew it was the capacitors that smelled and not a combination of resistors/pcb/caps you replaced? Burning electronics components all smell the same to me. I was also wondering, considering the high cost of resistors and shipping, why you didn't just buy new resistors and change them when it was evident they were getting hot? Maybe it would be a good idea to take some IPA and wipe the excess rosin, solder boogers off the board and clean it up after soldering? That's the way we did it in the military after a solder job. Stuck out in the middle of nowhere, we didn't have the DIY audio website on the inter webs to use, still had paper schematics and what not. I sure do miss those analog Simpson meters...
It seems that both resistors were overheated, the more overheated ended up at 4K8 and the red band blackened, the less overheated ended up at 4K9 without any other sign, maybe because it dissipated the heat better, its solder seems bigger in the picture.
On the other channel, both resistors measure 5K1, although they are 5% rated.
All based on that what said the OP and the pictures.
Very true, that was my hypothesis.
Unfortunately so far the OP is afraid of high voltages into the amp, which explains the absence of dynamic measurements.
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