What determines a transformer's suitability to a particular circuit design?

[Hoot Owl]

I'm aware a transformer has to match up with a circuit to some degree, but what are the relevant specifications and how close do they have to be?

 

This concerns an old amp I have - PCB circuit. Components are old and it's reputed to have design flaws (according internet experts😄). Sound is currently cutting in and out and changing volume too (no, I haven't cleaned it - would rather change it - long-term project). I'm wondering if I can buy a hand-wired board for a Marshall (they are sold on ebay) and stick it in mine. Both are 50-watt, EL34. Mine has reverb and 5 pre-amp tubes. The Marshall has no reverb and three pre's. I can do without reverb. Changing out the transformers makes it cost prohibitive. The amp I'm altering is reputed to have large transformers and with tubes that run at high plate voltage. My old one is a Bedrock 1200. The Marshall board is for a 2204. Both have the same control scheme of Master, Gain, Bass, Mid, Treble, Presence, with two inputs and both Power and Bypass switches. The back is more different but I'm not worried about that at this point.

Sorry, that's all I know. How close to possible is this change?

 

Secondary question:

I have a schematic and parts list for the Bedrock, and I just bought Valve Amplifiers, by Morgan Jones. Maybe in a year or ten🙄 I could develop a hand-wired board true to the original design. No clue how hard this will be.

Any thoughts?

Edited October 23, 2021 by Hoot Owl

[daddymack]

I know these guys...if anyone can sort you out, they can.

Based on your reported symptoms...have you changed the tubes recently?

[Hoot Owl]

9 hours ago, daddymack said:

I know these guys...if anyone can sort you out, they can.

Based on your reported symptoms...have you changed the tubes recently?

Yes. Tubes all tubes are new, though the amp has sat for a long time and there could be corrosion in the sockets. I could check that but here and now I'm exploring options for jettisoning the PCB board.

 

BTW, found some informative videos on YouTube:

 

 

 

The transformers in my chassis have identifying marks but they are mostly illegible - rusted over or never stamped clearly in the first place. Can a tech test these to find their specifications, or is that even necessary? I'm wondering if, since these are both EL34 50-watt amps, might it be safe to just swap the PCB board out for the hand-wired Marshall replica board and just roll with it? The Marshall board I would use would be a replica for a 2204 Marshall. Both amps have similar controls (Master, Gain, Bass, Mid, Treble, Presence, separate Power and Bypass switches, two Inputs, . I'd have to go without reverb, however. I'm just getting started in trying to figure this out.

[daddymack]

As I don't know your electronics skill level, it is hard to offer much insight.

I'm curious as to your decision to 'junk' the board and embark on what will undoubtedly be a long and educational process, without first determining exactly what is causing your primary issue.

Do you have the schematic from the Bedrock board itself? I would start there comparing it 'point to point' with the proposed Marshall schematic.  There are often many similarities and suddenly a 'left turn'....

As to converting from a PCB to a turret board? That is not something I would suggest to non-technical folks...I certainly would not attempt it myself {I'm 45 years 'off the bench', and take on amp repairs as a personal challenge to my antiquated skills}.

If you are doing this in order to learn, then go for it [that's kind of how I started]...be aware you obviously run a risk just assuming the one board will 'pin out' the same as the other....IMHO, highly unlikely, unless Bedrock copied the Marshal board down to the component value level.

On 10/22/2021 at 1:49 PM, Hoot Owl said:

 I just bought Valve Amplifiers, by Morgan Jones.

 Read the book...I'm sure it will be informative. [I am not familiar with it..the only Morgan Jones I know of is this guy: