Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: mistersnitz on January 02, 2023, 02:34:21 pm

Title: 20W single ended 1x12 combo with trem and reverb
Post by: mistersnitz on January 02, 2023, 02:34:21 pm

I've posted this before but my thread got corrupted so here is my current layout and schematic for my single ended amp loosely based off of Uncle Doug's Tremo-Verb build.

Title: Re: 20W single ended 1x12 combo with trem and reverb
Post by: TIMBO on January 09, 2023, 12:14:18 am

Have you built it?

Title: Re: 20W single ended 1x12 combo with trem and reverb
Post by: sluckey on January 09, 2023, 06:31:59 am

Layout... OT blue wire should connect to second filter cap.

Title: Re: 20W single ended 1x12 combo with trem and reverb
Post by: pdf64 on January 09, 2023, 10:49:46 am

470k grid stoppers + 470k shared grid leak is wonky.
Look at 6V6 manufacturer info; the limit on grid circuit resistance in self bias is 0.5M per valve. You are 3x over that.
The facility to reduce bias to zero seems rather poor practice.

Title: Re: 20W single ended 1x12 combo with trem and reverb
Post by: mistersnitz on January 14, 2023, 04:43:36 pm

Timbo I have not had the time to work on the project, hopefully soon. Also I wanted to get some feedback on the schematic and layout before starting anything.

Thanks Sluckey I will make the correction to the layout!

Title: Re: 20W single ended 1x12 combo with trem and reverb
Post by: TIMBO on January 15, 2023, 02:24:27 am

No worries
The reason I ask is I'm not really into SE amps although I have built a parallel SE with a pair of 6GW8's and it sounded great.
SE amps have their greats but generally low wattage 5-10w
Haven't heard what a SE 20w would sound like.

Title: Re: 20W single ended 1x12 combo with trem and reverb
Post by: shooter on January 15, 2023, 05:13:15 am

Quote

Haven't heard what a SE 20w would sound like.

fwiw, I've build a few in this range, the typical reply from the guitarist, that test drive for me;
"This thing is LOUD, this can't be a 20W amp"
most of mine are head-units through a 2 X12.

Title: Re: 20W single ended 1x12 combo with trem and reverb
Post by: tubeswell on January 15, 2023, 08:17:45 am

2 parallel 6L6s?

Title: Re: 20W single ended 1x12 combo with trem and reverb
Post by: shooter on January 15, 2023, 09:37:45 am

they ain't labeled
I get there with a single KT88, ~420vdc, dissipating ~42W, and ~60Vac ready to drive it, all the way to square-waves  :icon_biggrin:

Title: Re: 20W single ended 1x12 combo with trem and reverb
Post by: tubeswell on January 15, 2023, 10:17:33 pm

Quote from: shooter on January 15, 2023, 09:37:45 am

they ain't labeled
I get there with a single KT88, ~420vdc, dissipating ~42W, and ~60Vac ready to drive it, all the way to square-waves  :icon_biggrin:

Or 2 parallel 6L6GC fully driven with optimum efficiency

Title: Re: 20W single ended 1x12 combo with trem and reverb
Post by: kagliostro on January 16, 2023, 01:04:23 am

With 300V B + 250V G2 a GU50 in SE is able to perform 18W

As datasheet you can refer also to the EL152 (civil version of the LS50/GU50 tube)

(https://i.imgur.com/Nm0MHAz.jpg)

A friend is building a 2 x GU50 in PSE amp

(https://i.imgur.com/p3VzEOo.jpg)

(https://i.imgur.com/Xm8iM1o.jpg)


Franco

Title: Re: 20W single ended 1x12 combo with trem and reverb
Post by: Tirol29 on January 17, 2023, 01:12:04 pm

hello,
what will happen when V5 or V6 bias pot (2.5k) become a short ?

Title: Re: 20W single ended 1x12 combo with trem and reverb
Post by: sluckey on January 17, 2023, 01:16:32 pm

Tubes will quickly die.

Title: Re: 20W single ended 1x12 combo with trem and reverb
Post by: kagliostro on January 19, 2023, 09:39:37 am

I never tried but this seems a better way to have an adjustable Cathode Bias

Franco

Title: Re: 20W single ended 1x12 combo with trem and reverb
Post by: jordan86 on January 20, 2023, 09:09:10 am

Quote from: kagliostro on January 19, 2023, 09:39:37 am

I never tried but this seems a better way to have an adjustable Cathode Bias

Franco

This looks like the ax84 layout. I have this in one of their SEL builds that I’ve tweaked into a more plexi preamp. It works very well. I had a bad tube that burnt up the original 2W pot and replaced with a 5W wirewound CTS pot a few years back. I believe it is 1K. I can bias anything from a 6V6 to a KT88.