5-10 repair/restoration question, output transformer.

[Valvepower]

Hello,

Been pondering if I should post this or not, however here goes…

I’m restoring of a couple Specto 5-10 amplifiers and was going to get a couple of transformers rewound to exactly match the original 5-10 transformer specification as used by Specto… The 'replacement' transformers currently fitted are not up to the original 5-10 specification and are more of what I'd call a 'guitar' amplifier design.

I have a couple of Parmeko Model P2629 transformers (these are listed in the Mullard 5-10 information) in the workshop I bagged at jumbles and swapmeets and I could use those, but they are a drop-through design so to do a neat and tidy job it would necessitate the cutting of a hole in the chassis; alright I could mount it ‘terminals up’ by removing the Parmeko fitted shrouds and use two transformer frames to mount the transformers or even fitting standard shrouds and hard wire the transformer.

The question is…, would cutting a hole and properly mounting the transformer – as intended by Parmeko – devalue the amplifier?

In the past I’d have just gone ahead, however with a few recent discussions of leaving equipment as near as original, would fitting the Parmeko be seen as ‘not the right thing to do’… If it were a Constable painting, then it would be a different thing, but these a ‘work-a-day’ Specto 5-10 amplifier!

In some way using the Parmeko as intended could be seen as a 'sensible period’ repair. The Parmeko can be seen as better part as all the Specto output transformers I’ve encountered have had a o/cct primary winding, plus I won’t have the expense of getting the original transformers rewound.

Terry

[GrimJosef]

You could sit the Parmekos on spacers made out of Tufnol thick enough to keep the terminals above the chassis then run the wiring from them down through the chassis (presumably there's a grommetted hole or two ?). If the chassis is steel then the resulting gap between it and the transformer iron might reduce any hum coupling too.

Cheers,

GJ

[G6Tanuki]

Yes, you could cut a flat square block of something suitably thick - it doesnt have to be an insulator - then mill out the centre so the terminals and wires can fit through, then use long bolts to sandwich the block between the transformer mounting-lugs and the chassis.

[Radio Wrangler]

Don't forget insulating bushes on through bolts, otherwise you can get shorted part-turns as you can get flux around the bolt and bolts shorted together by end-bell and chassis.

David

[Uncle Bulgaria]

Have you considered some new top-mounted transformers? Primary Windings and others make 5-10 transformers new in the UK.

[Valvepower]

Hello,

Thanks for the replies – really appreciated.

I’ve decided not to cut the chassis about and do what I call reversible work, so if desired an original rewound part can be fitted and I'll look at mounting the transformer on the chassis using some sort of spacer(s) etc.

Interesting point about using insulating bushes to eliminate flux generated issues around the mounting bolts – I would have assumed there would be minimal flux around the mounting bolts. Anyway, I have some M3 and M4 Nylon spacers I can use.

Uncle Bulgaria, the aim was to use period output transformers in these Specto amplifiers, however I agree there is some nice ‘new’ transformers available. I actually have a pair of Primary Windings 5-10 (with single 8 Ohm tap) output transformers in the workshop for another commercial project, which is on hold at moment.

Terry

[Radio Wrangler]

Sometimes you get appreciable flux around mounting bolts going through holes in lams. You can get several amps in the bolts. It's due to an imbalance between flux passing bolt hole on one side to that on the other.

David

[Ed_Dinning]

The effect of bolt heating is more prevalent on mains transformers that run at higher flux levels. It would be unlikely to give significant heating on an output transformer, but may have an affect on distortion levels.
Fitting bolt insulation will do no harm.

Ed