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need help with 100W 1969 assembly
Posted: Tue Apr 17, 2018 11:53 am
by no0sand1s
Hello all. I recently completed assembly of a 1969 100W amp and during initial testing, I am getting unusual readings on my meter for voltage on the tube sockets. I obtain 3.47VDC for measurements on pin 2/7 of V4, V5, V6, and V7 and have adjusted the bias trim pot to obtain -49VDC.
The forum is not accepting uploads - here's a link to photos: If anyone has ideas where to take a peek or sees anything I missed, please let me know. If additional photos are necessary, please advise. The forum is not accepting uploads - here's a link to photos:
https://www.flickr.com/gp/wedinbordeaux/hGVA62
Thanks!
no0sand1s
Re: need help with 100W 1969 assembly
Posted: Fri Aug 02, 2019 1:07 pm
by casadenat
Going to resurrect this one. I’m not the original poster but I too am having problems with my 69 super lead build. My voltages are all close . All my power tubes glow but I have little to no output. Only a whisper can be heard. Chopstick the amp and cant find a short. Reflowed solder but still nothing. I’m losing my mind. Can someone talk me through this???
Re: need help with 100W 1969 assembly
Posted: Tue Jan 14, 2020 12:32 pm
by wdelaney72
casadenat wrote: ↑Fri Aug 02, 2019 1:07 pm
Going to resurrect this one. I’m not the original poster but I too am having problems with my 69 super lead build. My voltages are all close . All my power tubes glow but I have little to no output. Only a whisper can be heard. Chopstick the amp and cant find a short. Reflowed solder but still nothing. I’m losing my mind. Can someone talk me through this???
You should hear a bit of hiss / air after the standby is on. If you do guessing something is not connected. Using a multimeter, you will want to do continuity tests between points throughout the pre-amp. Something is likely not connected or you are grounding out somewhere.
If you have absolutely no audible hiss of any kind at all, your power section is likely a poblem.
Gotta get some pics of the wiring up to help you walk through.
Re: need help with 100W 1969 assembly
Posted: Tue Jan 14, 2020 5:37 pm
by danman
There is a 470 ohm resistor cathode resistor on the board between two 1 megs. It's a common mistake in new builds to install a 470k resistor there by accident. This results in the exact same issues you are having. If the color codes are hard to read, lift one end of the resistor from the turret and check it with your meter.