lassoharp said:
But of the same quality is the question. And if less, how much less. I imagine the bass response will be the first to suffer as the price drops. Maybe we need CJ in on this thread for some DIY advice on winding our own plate chokes.
Yes, using something of dubious quality would be wrong, I agree.
The bass response is determined by core saturation and the inductance value and impedance in relation the the impedance of the valve so, if 72H is listed on the schematic, 100H and up would cover it. Even bigger is OK too in my opinion.
I've no idea what the DCR of the original is but it probably wasn't massive given the inductance value - a V72 choke is over 10K DCR for instance but it's also several hundred henries L. I see there's also a 5K resistor in series with the choke which would add to the DCR for the voltage dropped to the anode.
Capacitance should really be low for good high end response so that's probably where a cheap unit would fall down.
From the Sowter site, the one suggested above is designed for 100mA DC current which is a LOT ;D . I would think the output valve in the RS61 is operated at 7 or 8mA given the 10:1 output transformer ratio.
I do know that Cinemag make an anode choke and 10:1 output transformer for a commercial product but I've no idea on price, the availability or not to us mere mortals or what the model numbers are.
lassoharp said:
The real compromise for a clone IMO is lack of the original I/O transformers. Brian Sowter would probably gladly rev engineer one. You'd probably have to feed someone knock out drops to get a donor though. ;D
I have some internal pictures of the RS61 I owned (I think I might have posted one or two here but I'll look around) but I have no idea of the transformer winding data other than the EMI part numbers. And I only know of 3 original amp units - the two that the guy is trying to sell on the Bay for $60K and the one that I sold and is now in the US.
We would probably need knock out drops intended for elephants to get hold of one of those
Or the same amount of money it would cost to buy an elephant so we can get that pair from Ebay.
Too bad Edcor don't do chokes.
At present, I'd go for Lundahl or give those on Ebay a try but someone should contact Brian Sowter or Cinemag to see about something that's about 100H, good for 10mA or a bit more and has low capacitance.