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On Friday, March 4, 2022 at 1:47:59 PM UTC-5, ohg...@gmail.com wrote:
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.
No 5-volt rectifier winding, so a pretty basic device.
https://www.hammfg.com/electronics/transformers/classic/290
I see several options that bracket your numbers. Pricing looks like US$120 - US$150, or so. Looks like lead time (up to 9 weeks) may be a stumbling block.
https://www.mercurymagnetics.com/make/ampeg/ Another option. Looks a bit pricier.
The internet is your friend.
Peter Wieck
Melrose Park, PA
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).
ohg...@gmail.com wrote:
=====================> > 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).
** 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.
...... Phil
** 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.
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?
ohg...@gmail.com wrote:
======================
** 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.
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?
** 7 or 8 amps .
. I didn\'t check the electros yet
** Replacement is over due if they are originals.
but from what I\'ve read, the power transformers are known to be weak.
** You say the primary is open - which is quite unusual.
Only time you see that is when there is an internal thermal fuse in series and the tranny reaches the critical temp.
..... Phil
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).
Best of luck with it.
Peter Wieck
Melrose Park, PA
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.
ohg...@gmail.com wrote:
======================
ed.
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.
** Don\'t think you need two.
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.
..... Phil