terma_reverb
Joined: Apr 17, 2012
Posts: 9
Heraklion Crete
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Posted on Mar 16 2023 07:11 AM
Hello everyone. I don't post much here but I wanted to share my first amp build which is based on 6G14A Showman, I call it the "Big Brownie". It is the clean channel with the power amp circuit of a 6G14A Showman, minus the vibrato channel, plus some more modifications to make it a bit more versatile:
- mid control
- master volume
- low cut and bias switch at the preamp
- adjustable/switchable negative feedback
- adjustable output transformer impedance (4, 8, 16 Ohm)
I used a Princeton reverb chassis. The amp head is build by me, while the speaker cabinet is built by Colorsound boutique amps. I have load it with a Weber Neomag 15". I started this project about 10 months ago with almost zero knowledge and experience on tube amps, so please be gentle. The head cabinet has some obvious imperfections but I plan to try another take in the future. Needless to say it sounds awesome! I hope I can provide some sound samples soon.
— Fountoukia - storm surf from Crete, Greece
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slingshotdragster
Joined: Jun 13, 2009
Posts: 70
Adelaide, South Australia
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Posted on Mar 16 2023 09:10 AM
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DeathTide
Joined: Apr 13, 2018
Posts: 1139
New Orleans
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Posted on Mar 16 2023 09:23 AM
Beautiful!
— Daniel Deathtide
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Tqi
Joined: Dec 07, 2014
Posts: 845
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Posted on Mar 16 2023 06:57 PM
Can you tell use more about it? What transformers did you use? Did you make a custom chassis?
— - "The Mysterious" Tqi.
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DrippyReverbTremolo
Joined: Mar 11, 2023
Posts: 15
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Posted on Mar 17 2023 12:46 AM
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terma_reverb
Joined: Apr 17, 2012
Posts: 9
Heraklion Crete
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Posted on Mar 18 2023 01:30 AM
Thanks for the nice words everyone!
I used this output transformer, which can be used as a replacement for 125A4A that matches the Fender schematic.
For the power transformer I ordered it from a local builder which costed me a lot cheaper than ordering online. The specs are 320-0-320V @ 440mA for HT, 60V for bias, 3.15-0-3.15 @ 5A for the heaters. The measured voltages are a bit lower than the ones in the schematic, but still in the acceptable range.
I used a bare Princeton reverb chassis in which I drilled my own layout. Drilling the chassis was one of the hardest parts of this project...
I used carbon comb resistors pretty much everywhere except from the voltage filters and power tube screens. I used Spague capacitors for the voltage filters and Sozo Blue Molded for the rest of the circuit.
References to the modifications I did can be found here, (thanks to Rob Robinette):
Master volume (Lar-Mar Type 2)
Middle control (as in Rob Robinette's Blackvibe)
Bias switch
Adjustable negative feedback
Adjustable bias using two bias pots
Stand-by pop reduction
I also accounted for the vibrato channel load as Rob Robinette does in Blackvibe.
For the frontplate and backplate, I designed them at Inkscape. I painted brown two aluminum pieces and then I went to local store to screen print the letters.
— Fountoukia - storm surf from Crete, Greece
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Tqi
Joined: Dec 07, 2014
Posts: 845
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Posted on Mar 18 2023 02:54 AM
terma_reverb wrote:
Thanks for the nice words everyone!
I used this output transformer, which can be used as a replacement for 125A4A that matches the Fender schematic.
Finally, someone used the Heyboer 45268-1. I have one sat on my chassis waiting for the local hackerspace to answer my texts about joining. Can you share some samples of how great your amp sounds? Preferably with a Jaguar and a Surfy Bear if you have them. ;)
For the power transformer I ordered it from a local builder which costed me a lot cheaper than ordering online.
I thought about doing that because my tubes are a little hungrier than western ones and I'm worried about going over the heater current. Can't get them to get back to me, either.
I used carbon comb resistors pretty much everywhere except from the voltage filters and power tube screens. I used Spague capacitors for the voltage filters and Sozo Blue Molded for the rest of the circuit.
Very vintage! I used cheap carbon film and literally whatever axial caps I could find. We'll find out how bad that sounds... eventually!
(thanks to Rob Robinette)
The man is a king.
For the frontplate and backplate, I designed them at Inkscape.
That software is also a king.
— - "The Mysterious" Tqi.
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kick_the_reverb
Joined: Feb 26, 2006
Posts: 1274
Escondido, CA
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Posted on Mar 18 2023 01:55 PM
Cool build terma_reverb, thanks for sharing!
Tqi - I had this OT installed in one of my Showman amps (a 61 that I bought with an un-original black panel era OT, so I can turn it into a double Showman with no remorse).
I foolishly bought it from TAD (I am in the US), because I wasn't aware Mojotone sells the same thing for much less.
In any case, it sounds good, and has held up so far.
Good luck with yours!
Ran
Tqi wrote:
terma_reverb wrote:
Thanks for the nice words everyone!
I used this output transformer, which can be used as a replacement for 125A4A that matches the Fender schematic.
Finally, someone used the Heyboer 45268-1. I have one sat on my chassis waiting for the local hackerspace to answer my texts about joining. Can you share some samples of how great your amp sounds? Preferably with a Jaguar and a Surfy Bear if you have them. ;)
— The Scimitars
Last edited: Mar 18, 2023 13:56:19
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terma_reverb
Joined: Apr 17, 2012
Posts: 9
Heraklion Crete
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Posted on Mar 19 2023 08:23 AM
Finally, someone used the Heyboer 45268-1
I did not have a clue that this is the manufacturer, thanks for the info!
Can you share some samples of how great your amp sounds? Preferably with a Jaguar and a Surfy Bear if you have them
I plan to record some proper samples in a studio. I will share as soon as I have them. I have a Strat however, but I think you'll get the point! 
Very vintage! I used cheap carbon film and literally whatever axial caps I could find. We'll find out how bad that sounds... eventually!
Don't rely only in the quality of the parts, also strive for quality of work. Even though I use quality parts, I have some noise issues that I am still trying to fix - mostly caused by improper joints due to my weak soldering skills. But I guess that this is part of the process. I think that with patience and special care your amp will sound great, it might just sound differently great. 
— Fountoukia - storm surf from Crete, Greece
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