Yeah don't replace those Output transistors now. Maybe later if they prove to be faulty but only then. You have already narrowed the problem to being on the preamp side of the amp. Perhaps there is a problem on the output side too, but there is DEFINITELY a problem that needs to be fixed on the preamp. Signal tracing and voltage readings will be your best friend right now. Hey you might end up fixing the preamp to find the amp working normal again. Don't shot gun this thing seriously.

Quote from: Vitrolin on September 04, 2016, 01:57:06 PM
where are you going to use them?
without that information it will be hard to find a substitute..

Lets play the guessing game??? Polytone??  :duh :duh

Quote from: g1 on July 23, 2016, 03:55:06 PMR29 has not been modified, it matches what the schematic shows.
I would guess there was an error or change in the board layout that had to be corrected by moving one end of R29.  If R29 was placed as the silkscreening shows, it would connect to TR8, rather than TR7.

Sorry about that one. It was late when I was looking at the picture and trying to match it up to the schematic. I should not have assumed it was not stock that way and thanks for setting my comment straight.

I would curious why R29 was modified and it might be best to put amp back to stock before any modding. The idea is to get it back to how it was designed and then think about modding at that point. Also, TR3 looks like a chunk of it has blown out by the looks of the pic.

Just have to ask what you are planning to build? Seems we are jumping around a bit on the tube type questions with little information for what this tube amp's designed purpose will serve. There is your intended use for what you want to build or research and that is what is most important really.

What worries me the most is if any of these forums were to lose the archive data it works hard to protect. So much useful information to pass along in search form. We saw that happen with the database crash and lost many years worth of pictures & schematics uploads.

No point creating another "what happened to MEF threads"... I think I will just tack something on here... So? It appears that the server is not connected to the Internet or something. Typically in the past it would come up with a Database Error page or something or another. This time it appears to be truly offline. I am sure it will be up again, but any time it disappears it worries me a bit. I probably worry too much though. Anyone know what's going on?

Quote from: Vitrolin on July 14, 2016, 03:36:49 PMremember that the output power claimed is depending on the THD level accepted, 24W maybe be with how much distortion?

24 watts at 10% THD or higher would be my guess.

Also here is a jim Kelly amp that uses 4 6v6 tubes on the output...


http://www.themusiczoo.com/product/15489/John-Suhr-Amplifiers-Jim-Kelley-Single-Channel-Reverb-Amplifier-Head/

Still not finding any schematics but would not be hard to design this amp. Finding a good match for the Output Transformer would be my greatest concern right off the bat. 

I attached the schematic...

The 6v6 data sheets are your best friend. 6V6GT in a champ Single Ended is roughly about 5 watts and this can vary slightly. If you have two 6V6 tubes in push/pull AB it is conservatively about 10-14 watts, but it can be higher like 15-18 watts. Some claim that they can get 24 watts out of a pair 6v6 push/pull AB. My feeling is that you'll be eating through tubes if you push the thing that far. I guess a 40 watt amp is not out the question (push/pull AB) running 4 6v6gt tubes, but I am having trouble finding a decent schematic to reference.

Honestly that first 3 transistor amp schematic was just awful really. I saw this one and thought this is a way better way to do it. At least build this one with what you have and analyze how it all works. Then at that point build a 15 watt guy.

http://www.deeptronic.com/small-audio-power-amplifier-using-3-transistors/

Those two diodes bias Q1 and Q2. So it could be that eliminating one from the circuit makes for a colder bias, and the result is cross over distortion.

Quote from: Hawk on May 24, 2016, 12:01:24 PM
Single black band? A resistor?

A zero ohm resistor or essentially a piece of jumper wire.

https://en.wikipedia.org/wiki/Zero-ohm_link

http://www.tangible-technology.com/schematics/marshall/DSL/DSL15C/DSL40C/

Quote from: Vitrolin on April 27, 2016, 12:51:37 PMcapacitors shouldn't get hot, my guess is that its shorted.
wich capacitor is getting hot?
with your amp turned off, take your meter and measure the resistance or conductivity of the capacitor.

Which capacitor is it in relation to the schematic? Also, please be aware that you want to test the caps for any stored charge before you test any resistances with your meter. You will need to drain the caps first before testing for resistance.