Cloning An SV20

[audiosalvage]

Wow, I thought that was the genuine schematic. I probably will stick to the 1959/1987 preamp topology. And just wing the power section. Isn't that what this is modeled after anyway, ie Van Halen, Hendrix etc.

 

[Gene Ballzz]

@Pete Farrington and all other interested parties,
Here's the deal and a question.

My goal is to develop an easy to build version of the SV20, with all of it's tonal characteristics, but trimmed down and simplified in the following manner:
> Easily repairable and modified turret board construction.
> 20 watt mode only, as the lower wattage mode only nets a -4db to -5db reduction in volume, with a small (but noticeable) loss in dynamics.
> Elimination of all low voltage relays and solid state devices, to simplify the power transformer and power supply configuration.
> A somewhat improved effects loop (ala Metro or Granger), powered from some point of the B+ rail instead of the low voltage SV20 effects loop.
> All else should be a near duplicate of the SV20 design and schematic.
> It should be noted that I have an SV20 on hand for testing, voltage surveys, etc,

And now the question:
"Should I continue this already kinda lengthy thread, with al of it's side tracks, or should or start a new thread?"

Thanks Folks,
Gene

 

[gldtp99]

Sounds like you've got a good plan

The build itself seems pretty straightforward

The turret board construction, simpler FX Loop (Metro, etc) and a PPIMV all seem like good ideas to me
( maybe an attenuator would work better than a PPIMV on a NMV type Marshall --- I don't like the PPIMV I put in my older build 1987 clone)

An aggressive model 1987-type preamp (w/4700pF bright cap) and a .0033uF coupling cap (nor far from the .0022uF coupling cap used in some 1987/1959 amps)

Cathode biased EL34 outputs

In the two mini-2204 heads I've recently built I built them Fixed Bias --- but either way would work, it's neither here nor there

What iron are you using ? (PT and OT) ??

 

[Gene Ballzz]

Sounds like you've got a good plan

The build itself seems pretty straightforward

The turret board construction, simpler FX Loop (Metro, etc) and a PPIMV all seem like good ideas to me
( maybe an attenuator would work better than a PPIMV on a NMV type Marshall --- I don't like the PPIMV I put in my older build 1987 clone)

A PPIMV is not intended and has never been mentioned by me. A great @JohnH M2 attenuator and an amp like this are a match made in heaven!

An aggressive model 1987-type preamp (w/4700pF bright cap) and a .0033uF coupling cap (nor far from the .0022uF coupling cap used in some 1987/1959 amps)

Cathode biased EL34 outputs

In the two mini-2204 heads I've recently built I built them Fixed Bias --- but either way would work, it's neither here nor there

What iron are you using ? (PT and OT) ??

Ahhh, the iron! There's the rub, as always, isn't it? The right or wrong iron can make or break any amp build! I believe one of the biggest challenges here will be determining and "finding" just the right iron!

Thanks For Replyin'
Gene

 

[gldtp99]

FWIW --- I used a new Edcor XPWR013 PT for my 2nd mini-2204 build:

https://edcorusa.com/products/xpwr0...1&_sid=d4365ac62&_ss=r&variant=41177682051259

It has a rated current capacity of 120mA and gives @360V B+ w/solid state rectifier in my amp --- Just about right for a 20-25 watt mini Marshall

I used an old PT I pulled from a 1950's Stromberg-Carlson PA head that ran two metal 6L6 tubes in cathode bias --- It has a 6.6k primary and 4/8/16 ohm secondaries --- The amp was rated 20 watts output --- this amp is a highly modded 2204-ish amp based on an old Roccaforte HG100 schematic --- It runs well and is impressive sounding --- I played it this morning

My earlier mini-2204 (near stock) build uses a Classic Tone 40-18087 OT (their Fat Stack Deluxe Reverb OT w/4/8/16 output taps --- also has a 6.6k primary) --- also a good choice for a 20-25 watt Marshall--- This amp also runs 6L6GC x 2/fixed bias --- Amp Parts Direct sells a Heyboer OT with similar specs (I don't think the Classic Tone is still available):

Fender Deluxe Style, 20W Output Transformer Upgrade 4/8/16 Ohm - APD-8087H

Heyboer Transformers®Premium guitar amplifier power transformers, output transformers and chokes.Proudly manufactured in the U.S.A. Our Part# OEM Part# Series Type Rating APD-8087H HTS-13226-APD Plus Output 20W 6.6K to 4/8/16 ohm Alternates: None Classictone Classictone.net Classictone...

shop.amppartsdirect.com

EL34's will happily run into a 6.6k load (especially for lower power)

EL34's will run into a range of OT primary loads as seen in Duncan's Tube Info:

TDSL Tube data [EL34]

PS ---- I'm just sharing some of my experiences in building 20-25 watt Marshalls lately --- You are certainly free to make your own decisions on transformers for your build