18 watt output issue

[dixiepig]

Greetings from Virginia;

I recently tried my hand at building my first tube amp. The 18 Watt Stout w/gain switch. In the past I have built several solid state amps with pretty good success, I don't over expect since its just a hobby with me. Anyhow I assembled the amplifier, plugged it in, flipped the switch and low and behold sound came out of the "test" speaker. I was pretty satisfied at that point BUT. when I attemped to adjust the Volume and/or Tone pots there was no change in either level. I have been back over the wiring several times and cannot locate an issue. I have removed and tested both pots (they work). I have even tried other speakers. also the tubes are new. I was debating on bypassing the relay completely to see if it made a difference but decided to try this forum first.

I do need to confess to one screw up which may or may not make a difference. The output transformer I used is rated at 6.8K on the primary side (8 ohm secondary). I used this transformer basically because it was rated at 20 watts and was a direct replacement for a Fender amp (Hammond 1750H). During further reading/investigation I saw where this design was based on an 18 watt Marshall and the output transformer specified for that amp has 8k on the primary side. since this is the first time I have messed with an output transformer I am not sure what I have opened my self up for.

1) any ideas on the volume/tone problem.

2) how bad have I screwed up with the OT.

[Willabe]

Hi, dixiepig.

6.8K instead of 8K on your OT primary is not why your volume and tone pot/s are not working. You did'nt mess up any thing by using a 6.8K instead of a 8K. There are a # of past posts in here that go into detail on that subject, do a search, you'll find them.

Sounds like you've miswired something or a bad solder joint. The amp puts out sound, thats good, so it seems like it's in the volume/tone pots wiring.

Look again and check your solder connections. If the pots are'nt grounded right they wont work. Reflow there ground solder joints.



  
                     Brad        

[dixiepig]

Finally got it! the 1M resistor at the input was grounding out at the jack. GEZ that took long enough. Anyway this design actually sounds better than I had hoped. thanks for the advice Willabe!

[Willabe]

Glad you found it.

            Brad