John Mayer Signature New Build with Reverb Issue

[dorrisant]

I've been working on this build for a while now. Epi SoCal 50 donor chassis, iron and headshell. I cut out the offending chassis top and replaced with new aluminum. I did my own layout. .

This thing sounds glorious... As long as I keep the reverb return pot down, barely cracked at all. It sounds good there, sounds like the reverb hall from hell above that. I noticed the floating ground for the tank return on the schematics posted so I tried that. That was an ear piercing experience.

It seems the effects loop is too sensitive as well. I've checked through component values and connections a few times but I could be missing something.

I'm wondering if any of you guys that have built these have encountered anything like this. Or if anyone else had any suggestions please do so.

As it is:
50 watt layout
Voltages seem to be in line with know good clones
DC filaments on the preamp tubes
Bias circuit is on a separate PT tap
Totally different layout
No hum off hiss (OT had to be there)
Need to etch the front and back plates yet

Many thanks to mhartman, Aaron and Mark Fowler for the great info and posts. Thanks to Taylor for the tolex tutorial. Sorry if I left anyone out!

I can post more (specific) pics or info if needed, just ask.

Tony

[beasleybodyshop]

Woah! looks good Dorrisant. did you alter the layout due to chassis size? I made mine a few inches longer to give some breathing room. What was the thought on using DC heaters in your build? Reverb sensitivity?

also i see you went with a resistor instead of a choke. was that for space reasons?

[M Fowler]

Very sweet looking built sorry it has some issues. Maybe the wiring of the reverb pot.

[dorrisant]

Thanks guys!

The Epi PT had a tap for DC heaters and it should be quieter so I just went ahead and used it. Also, I did use the choke that came with the original amp... You just can't see it in the pics I posted. Yes, I wanted to use up the space behind the pots a little better so I spaced it out a bit. I left the local feedback loop for the first stage right there at the tube socket.

Tony

[Reeltarded]

Tony it looks fantastic! i like the outside as much as the inside. Dumble Thundedome!!

[dorrisant]

My phone loves to double post.

Tony

[srvbaker]

Hey mate
I have build that amp just recently too, and could not even fathom turning the reverb send and return over 3, otherwise it would wash out massively. I've ordered 3 different triode variations for different gain charactoristics and after that will play with voltages.

But Taylor from amplified nation suggested to me to try a cap from the send pot input to ground to dump some signal. I think I used 0.05uF or something like that but it really set the reverb way back in the mix and gave me useable range with the reverb controls. Play around with the cap values. I also added 120pf across the master to brighten it up a bit but that was just personal taste and I'm yet to play with other values there too.

Hope this helps a bit

Thanks to Taylor for that fix

[srvbaker]

Also, the schematic shows a 10k resistor from whatever power supply node to the reverb transformer, but no cap at the transformer. I found a 22uF electrolytic tightened things up a bit, but again that was personal preference

[beasleybodyshop]

Mark, did you find the same issue with your reverb? Was it too overpowering?

[M Fowler]

Mark, did you find the same issue with your reverb? Was it too overpowering?

No I didn't.

[dorrisant]

Hey mate
I have build that amp just recently too, and could not even fathom turning the reverb send and return over 3, otherwise it would wash out massively. I've ordered 3 different triode variations for different gain charactoristics and after that will play with voltages.

But Taylor from amplified nation suggested to me to try a cap from the send pot input to ground to dump some signal. I think I used 0.05uF or something like that but it really set the reverb way back in the mix and gave me useable range with the reverb controls. Play around with the cap values. I also added 120pf across the master to brighten it up a bit but that was just personal taste and I'm yet to play with other values there too.

Hope this helps a bit

Thanks to Taylor for that fix

Yes... I will try this. Thanks a bunch!

Tony

[M Fowler]

I wired my amp like the schematic shown on page 2. https://tubeamparchive.com/viewtopic.php?t=21917

[beasleybodyshop]

Mark and Tony,

What plate voltages are you seeing in your builds? I've been wanting to use a quad of tung sol 5881s but don't know if the plates are going to be high

[dorrisant]

441 with the Epi iron.

[dorrisant]

Thanks srvbaker! I used a decade box to dial in the right value, .07 or so works great. Now there is much more useful range to the return pot.

Now I have to adjust the bias circuit a bit... I can only get a max of about 60% as it is. I'll get that tweaked and let it cook for a while.

Tony