Traynor YVM-1 Conversion to Guitar Amp Suggestions

[misterc57]

Hey Folks

I want to convert this amp to a guitar amp and looking for suggestions.

This amp has (2) EL34 and (4) 12AX7 and huge iron.

I plan to remove the four back panel input jacks and the first two volume pots (change those first two pots to a hi and low input). Remove outputs 3 and 4 and only have two output jacks.

I'm thinking maybe do a preamp similar to a JCM800 4010. I may be able to bypass V1.

I want to make the most use of what is there and not go crazy with changes. Is this as simple as modifying the input jacks or is there more stage coupling considerations?

Schematic attached of Traynor and JCM800

Thoughts and suggestions please!

Thank you.

Marshall-JCM800-50W-4010-Schematic.pdf

[Jon Snell]

It is already a guitar amp. I would enjoy the powerful sound .. or
Use a pedal to get distortion, if that is what you want.

[Chuck H]

It is already a guitar amp. I would enjoy the powerful sound .. or
Use a pedal to get distortion, if that is what you want.

It's actually a four channel PA with a universal effects loop and tone stack. Much could be changed to make it more like a typical guitar amp.

[Chuck H]

I built a guitar amp from one of those once but I did a full gut job on it. The stages aren't arranged anything like what we know as guitar amps so while you do have the tubes, sockets, chassis, transformers, etc. and they are already mounted it's my opinion that that is all you have. Which isn't a bad start. so you can choose just about any design that your tube compliment will handle.

[mozz]

Convert 2 channels to cathode bias and make some jumpers.

[Pedro Vecino]

I find the eq quite extravagant. The one on the Ampeg Portaflex (right) is much better centered.

[Helmholtz]

I don't think a flat response is desirable with a guitar amp conversion..

[Pedro Vecino]

The center position I show is just the starting point. The movement of the bass and treble curves and their relationships also seems quite strange to me on that amp.
On the Orange 80, 120, etc., while it doesn't have the linearity of the Portaflex in the center settings (that's a secondary thing for guitar) I find it more predictable and it is proven to work very well.
I don't know that amp but with that input configuration it suggests it's a PA amp (that's what led me to see how their equalization works).

[g1]

I don't know that amp but with that input configuration it suggests it's a PA amp (that's what led me to see how their equalization works).

Yes. It's hard to see on the front panel, but YVM stands for Yorkville Voice Master.

[misterc57]

I'm planning to go with a JCM800 preamp like section. Looking at the first stage.

The Traynor has no ground on the board and it was relying on the input jacks for ground. They do this in later stages also on the loop jack.

Now that I am moving two input jacks to the front and need ground for those jacks and preamp tubes I am looking for suggestions on perhaps making a preamp ground bus that I could attach to unused sections of the board, or other ground suggestions.

edit. I do not have a large enough iron to make a solder connection to the chassis.

Thank you.

[Chuck H]

For a chassis ground you can just drill a hole and install a solder lug with a tooth washer. Clean bright the nut/washer area and use some anti ox grease. This is typical for aluminum chassis and I think it should work just as well (if not better) for steel. Aluminum oxides are completely insulative where iron oxides usually are not.

[g1]

Why not just let the input jacks ground to chassis like they were at the back?

[nevetslab]

Reading thru this post makes me want to pull the Traynor bass amp I have that originally had 6CA7 power tubes. I put in a pair of KT 88’s in along with a regulator tube (6L6GC) to feed the screen supply.

I came up with a different tube preamp that had far more control range than the stock YBA-1 (think that was the model).

I remember posting details on the project years ago . It sits under my desk to remind me to make time to again pick up from where I left off as I never cared for the very limited range the stick bass and treble controls and their extended controls did little

I found the post after searching thru Traynor YBA-1A amps and found this: Tone Control Stack Frequency Response for Traynor YBA-1A Mk II which was dated 8/14/2014. I haven’t yet physically built up the circuit as it needs an additional tube in the circuit. I got as far as punching the new hole for the tube and ordering the parts but haven’t taken the semi-stock tag board apart to add the new terminal board to build up the revised circuit.

So it goes with too much to do in the shop and distractions.

[misterc57]

Question on JCM800 half V1 cathode bias cap value of 0.68. I have 0.47 and 1.0 on hand. Which is better to use for now and what effect do these values have?

Thank you.

[g1]

I would suggest going with the 1uF. A 0.47 will reduce the bass even more than typical Marshall.