RS124 Output Transformer
- Thread starter StarTrucker
- Start date
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I don't know about your Hammond but the output transformer must be gapped because it feeds the output tubes DC power supply. Not all transformers can do that. It must also be able to pass quite high levels signals, if you want a clean low end.
oops, silly mistake, but can 10kCT:600 be used here with different output pad values?
No, the circuit is pushpull, the two currents cancel each other regarding the resulting magnetization. No gap necessary
You are right ! My bad
That definitely won't handle the power level cleanly and I doubt it handles the current, DC resistance is high meaning small gauge wire.
jazzcrisis
Well-known member
I don't recommend it. Tried it in a very similar 6CG7 push pull output stage and got the characteristic lack of low end of an underspec'd transformer. I also ordered their gapped BA2 output transformer which wasn't great in the stock RCA circuit it's advertised for either.
Ó Draighnáin
Well-known member
You might find a used Triad A-53 (used in the Limpander), which I think is about right. However, you might balk at the frequency range specified in the catalogue.
Rob Flinn
Well-known member
I initially built my pair with edcor o/p transformers that i had lying around. They worked but I think were slightly underspecced. I eventually used a pair of sowter outs that are great but not so easy to get now that Carnhill have taken them over. I think I was waiting at least 3 or 4 months for them to be delivered from first placing the order. I'm not even sure they still make them. A real shame the day Brian sold the company. 
I was about to place an order for two of them, and now I am not sure I still want to do so. They are quite expensive, too, and brexit is not helping !
Did you take any measurements ? Would be good to know the performance in a real use scenario, I have been meaning to try these for a while but the price just sounded too good to be true.
You mean the secondary resistance ?
I also have a vintage UTC HA-114 laying around which is specd at +23dBm output and has the correct impedance ratio.
The DC resistance is 720 ohm on each primary and 13 ohm on each secondary
Do you think this would work well with 6CG7 / 6SN7 in push pull ?
The DC primary resistance is pretty much the same as the Hammond 850LA but the secondary resistance with secondaries in series is about half.
I am also looking at Lundahl LL1689, but it's not specified what is the maximum primary DC current per side.
Is it something that could be derived by looking at DC resistances or other published parameters ?
The datasheet is marked as "To be completed" for several years...
I find in general audio transformers datasheets are rather vague which makes choosing the right transformer a painful exercise if you don't have a very deep knowledge.
Last order I placed was very quick to arrive, just a few weeks. Maybe they have managed to build up some stock ?I initially built my pair with edcor o/p transformers that i had lying around. They worked but I think were slightly underspecced. I eventually used a pair of sowter outs that are great but not so easy to get now that Carnhill have taken them over. I think I was waiting at least 3 or 4 months for them to be delivered from first placing the order. I'm not even sure they still make them. A real shame the day Brian sold the company.
Sowter 8650 should work too ? I believe it's used in the Thermionic Culture Phoenix that's also a Altec 436 type circuit with a 12AU7 type output tube.
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Ó Draighnáin
Well-known member
Not sure, but the catalogue indicates that it physically weights twice as much (1/2 lb compared to 1/4lb) even without any shielding (which the J series have). Metal mass counts for something?
Rob Flinn
Well-known member
If you look at their website it gives a list of the transformers that they prioritise making and the 436 output is not on it. Also they say their is a 90 day lead time.
The 12au7 is a different valve to a 6cg7 therefore the 8650 may not be optimal with a 6cg7.
I have ordered 3x products that were not on the list and to my surprise they all came quickly.
I guess is worth asking for a lead time before placing an order.
8650 specs 30mA per primary side so it should be good for the 6CG7 that has a max of 20 or so mA
The description says in fact is suitable for 6SN7 that is very similar to 6CG7
Which Edcor did you find was underspecced?I initially built my pair with edcor o/p transformers that i had lying around. They worked but I think were slightly underspecced. I eventually used a pair of sowter outs that are great but not so easy to get now that Carnhill have taken them over. I think I was waiting at least 3 or 4 months for them to be delivered from first placing the order. I'm not even sure they still make them. A real shame the day Brian sold the company.
