I have a V5 here with an open primary. This uses 4X 6550 outputs and supposedly the trans is a weak link. Does anyone know of a drop-in replacement? Three secondaries: 6.3 fil drawing 7.5 amps, B+ guessing around 400 - 450V and a bias supply winding (not sure of voltage). Thanks.
Thanks Peter, but I was actually hoping for an exact replacement and I did see both those options you linked. Guitar players are picky about the tone, and although I don't think I'd hear it, the difference in B+ might be an issue in tone and power as well, so I don't want to guess at what it should be. The schematic doesn't list voltages.
The Mercury option you linked has no bias winding so I'd have to add a small side trans for that, and they didn't list the filament supply current on the spec sheet. This amp runs 7.5 amps in the filament which is pretty stout. Mercury lists a trans for the SVT-100 which I *suspect* is the same trans, but they don't publish a spec sheet for it.
I don't see a Hammond with a 8 amp plus winding at all. The highest Hammond has that I can tell is 7 amp, and those examples ran a lot less B+. A Hammond would require a separate filament transformer.
Yes, I can piece this together but was hoping there was a drop-in replacement that didn't require modifying the amp. If it were mine, I would cobble it together certainly but it's not my amp.
** Connect a source of say 3-5VAC to the heater winding of your tranny. This should allow you to measure AC voltages for the secondary and bias windings. Find the ratios and scale up relative to 6.3 as needed. The secondary is gonna be about 325V with 0.7 amps capacity.
Hope the tubes and electros are all OK. 6550s are pricy.
Good idea to back feed the secondary. If I don't find a drop-in that's what I'll do to get close to the right B+. The 4 outs and the 3 preamp tubes will draw just under 7.5 amps on the filament. What's a safe current specification for the filament winding?
Regarding the tubes - the guy bought a complete set of brand new matched JJ 6550 and JJ 12AX7s to fix the stone dead problem.. Oh, well. He brought in his original set which were all Chinese 6550s and a mix of Sovtek and Groove Tube 12AX7s. I didn't check the electros yet but from what I've read, the power transformers are known to be weak.
If there's an internal fuse, I didn't see one, and I did look. I pulled the end caps off and there aren't any junctions for one that I saw. I've replaced a few thermal fuses in home stereo amps, but there's nothing inside this one I can locate. There was also no sign of any significant heating or arcing/burning and no smell of any kind.
Are you able to wind back and find where the visible wires are connected to the winding(s)? Might be a break there.
And, if the alternative is landfill, I have done this three (3) times, and been successful once (1- time): a) Obtain a high-voltage, high value capacitor (I used an aggregate value of 100uF @ 500VDC) b) While being exceedingly careful, charge it on your bench supply to full capacity. c) Discharge it across the open winding - again, using great care.
It *MIGHT* weld across the break. I was successful, in actuality, twice as far as the Ohm-meter measured. But failure was quick (not instant) when 'real' voltage was applied in one case. In the other, the transformer remains in regular, but not frequent service in a small tube power-amp (primary).
The connections from the windings to the leads are visible without peeling any layers, and they were fine. I'm going to pull the trans once more and give it one more look over in case I missed something that can be fixed.
I talked to the customer Saturday, and he isn't averse to using two transformers as this isn't a historic amplifier and accurate preservation isn't in play. He's just looking for a tube amp with some nads and this one should have plenty.
A power tranny meant for the Fender " Bassman 100 " ( eg 290FX ) ought to be OK. The +DC voltage is close to right, but you need to change the rectifier set up to " full wave".
An extra 2 amps of heater current current is not such a big issue, the voltage may drop a little to say 6.0VAC but the additional heat in the tranny is only 1.5 watts or so. The tap on the secondary will work for negative bias.