Monoblock blues part 2.

[catch29]

So I need to replace the MA-12's output transformer. There is a tran' on ebay similar size and wiring, it is from a Linear amp 30 amp. It has the same colour input wires, bl,bk,red,wh,yw, but the output wires are 1 pair yw/vt, 1 pair yw/grn quoted at 8ohm each. The MA-12 has grn(common), yw(3ohm), vt(15ohm).
The power tubes on the MA-12 are el84 & the Linear el34. Ht on the MA-12 is I think 300v & the Linear 400v.
So advice please. Can I use this tran' and how would I configure the output wires?.
Better still, does anyone out there have a beaten up MA-12 or S99 they could sell me the tran' from or the hole unit?. I wonder how much it would be to have the tran' re-wound?. I attach a photo of my sick one.
Any advice appreciated.    

[Ed_Dinning]

Hi, a fairly standard EL84 UL/PP output transformer , but of a decent size and quality.
New, similar, units are I think about £180. A rewind would probably come in at about £100

Ed

[Diabolical Artificer]

This might be a better fit - https://primarywindings.com/product/mull...ansformer/ there's a two week lead time though.

Andy.

[Ed_Dinning]

Looks like a good price

Ed

[catch29]

Thanks Andy, That's really helpful

[BusyBee]

It looks like a useful supplier Andy. Thanks

Tracy

[Diabolical Artificer]

Wotcha Tracy, hope your in good fettle. I've bought several OPT's from John @ Primary Windings and used them in several valve amp builds. They are very well wound with decent specs for a really good price. Primary & secondary windings are interleaved, primary's have high inductance and sufficient laminations for decent LF response, L leakage is low as is pri/sec C. Windings are well impregnated with varnish. I've tested them from 10hz up to 100khz, with NFB and a decent design I got 20hz to 45khz -1dB, not bad for about £100 each.

After leaving the EU cheap OPT's & other iron is harder to find, Toroidy in Poland - https://sklep.toroidy.pl/en_US/index is still good value but less so than previously due to customs fees & a weaker exchange rate etc.

Andy.

[joebog1]

Did you ever test my traffos Andy ?. It would be interesting to see someone elses results.

Joe

[Diabolical Artificer]

Test them how Joe? I think I tested the primary L, frequency and low frequency response at full whack, apart that I used my ears. The first pair I used to build the first 807 PPP AB1 amp, my mate has it on long term loan, he's a bit of an audiophile and says him and mates said that amp and by inference your OPT's were as good as if not better than any of the high end amps they'd heard.

The other pair I built into a 807 Class A PPP mixed fixed bias/cathode bias, 807's running at 500v HT g2 300v regulated. the 807's are driven by a 6BL7 LTP and DET20 front end. I've just tweeked it, increasing the coupling cap size/lowering the LF response and also reduced the open loop gain a lot. I've not tested it on the bench but it sounds very good but i have it running with no NFB at present, needs some more work but pushed for time.

At present I'm trying to get the attached amp up and running, I'm currently running two 6BG6GA's in PP AB1, driven by a 12BH7 LTP and triode strapped 6CL6, it's ok but again needs tweeking.

This all takes time which I'm a bit short of at present as mentioned.

Andy.

[joebog1]

Thanks Andy,
I was just curious as all that I sold I never got any feedback apart from "very happy ".
I dont think many went to techy types and were just plonked into existing designs.

Joe