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Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Shrad wrote ...
you could use something like a FAN7530 to get a stable B+ instead of a valve rectifier and oversized inductions...
there is always the debate of using or not using the old school filtering for B+ supplies, but sincerely, why woud we still do this while we have modern solutions? there are some ways to mix designs and get the best of both worlds
Yes, I have been considering other 'solutions' as far as power supply goes.
Part of the attraction, for me, is to only use valves, with no silicon, but there are plenty of other solutions. I'm not familiar with the FAN7530 myself, but I had considered some sort of SMPS.
For me, building a power supply with no resistors seems fun, and I'm doing a lot of experiments with inductors at the moment, but the main point here is to use what's available.
I have the big rectifier tube, and a couple of smaller ones which should also be up to the job, so it makes sense to me to use them for a valve amp, in the same way I'm using valves I found in the shed.
I also have a 'big' inductor in the shed. I've not dug it out and measured the inductance yet, but 'watch this space'
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Well, I've dug out the 'big' inductor in the shed, and the plate on it says 10H 180mA. I think it should be big enough to use for a choke
Now to see what big capacitors I can turn up. I don't want to buy any 'motor run' capacitors unless I have to, and old ones would probably look 'cooler'.
EDIT: I wonder what voltage it's good for. Any ideas? It does say '463V' but that looks like a catalogue number.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Ash Small wrote ...
Well, I've dug out the 'big' inductor in the shed, and the plate on it says 10H 180mA. I think it should be big enough to use for a choke
Now to see what big capacitors I can turn up. I don't want to buy any 'motor run' capacitors unless I have to, and old ones would probably look 'cooler'.
EDIT: I wonder what voltage it's good for. Any ideas? It does say '463V' but that looks like a catalogue number.
I think you could feel confident in that choke in a 350V supply, Ash. It's a nice one. Parmeko is the best.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Proud Mary wrote ...
I think you could feel confident in that choke in a 350V supply, Ash. It's a nice one. Parmeko is the best.
It looks a bit dry, not too bad, though. Should I soak it in oil, for example, or anything else?
It looks like it was originally impregnated with something. A lot of the 'traditional' mixes were, I suspect, linseed oil based. Maybe I should try that?....any ideas?
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Ash Small wrote ...
Proud Mary wrote ...
I think you could feel confident in that choke in a 350V supply, Ash. It's a nice one. Parmeko is the best.
It looks a bit dry, not too bad, though. Should I soak it in oil, for example, or anything else?
It looks like it was originally impregnated with something. A lot of the 'traditional' mixes were, I suspect, linseed oil based. Maybe I should try that?....any ideas?
It looks fine to me. I've got some very similar chokes and transformers from Parmeko, and I think that's just the normal look of the varnish. I'd give it a good wash and brush up, but I wouldn't soak it in oil or anything, as that might soften the varnish and damage the insulation.
If you've got a Megger, you could test the insulation between the windings and the core, but I wouldn't worry about it too much. If it looks in good condition, and hasn't been badly bashed or smell of burning, it's probably OK. Parmeko is the Rolls-Royce of transformers, after all.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
I've updated the first post in the thread with details of the mains transformer I found in the shed. I'd appreciate any relevant comments that anyone may have:
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Ash Small wrote ...
I've updated the first post in the thread with details of the mains transformer I found in the shed. I'd appreciate any relevant comments that anyone may have:
23, 17, 25, C, and the two lugs second row from lower right clearly form the Earth/Chassis rail running through various centre taps.
To find out what is what: make a map of all the winding resistances between the lugs, so you can see which windings are continuous with one another, and which are not.
Windings likely to be found on this transformer could include
LT secondaries
0V-6.3V - perhaps two of these, (standard heaters) 3.15V-0V-3.15V - perhaps one of these (reduced noise 6.3V heater supply) 0V -5V - very common for full wave rectifier heaters. 0V - 4V - another common one for old rectifier heaters.
Possible oddball windings for grid bias supplies etc
One or two centre-tapped secondaries for HT windings
Primary windings could include a lineup like this 10V - 0V- 210V - 220V - 230V - 240V - 250V
Once you've made your continuity map, stick 24V or so 50Hz on the lugs you most suspect of being the primaries, and measure the outputs appearing at all the different windings.
A bit of trial and error like this and you'll get it sorted without too much difficulty.
As for condition, once you've cleaned all that gunge from around the lugs, examine the state of the insulation of the paxolin board with a hand lens. Sniff for burning, smoke smells, which can linger on a transformer for years. If there's no sign of a past disaster, and all the connections from the windings to the tag board look solid, it will probably be a runner.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141
Every Parmeko transformer that I have come across has been over-engineered to be damaged it would need to have been REALLY abused don't know what the varnish/encapsulant is but it seems to last a very long time.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Proud Mary wrote ...
Primary windings could include a lineup like this 10V - 0V- 210V - 220V - 230V - 240V - 250V
Once you've made your continuity map, stick 24V or so 50Hz on the lugs you most suspect of being the primaries, and measure the outputs appearing at all the different windings.
A bit of trial and error like this and you'll get it sorted without too much difficulty.
As for condition, once you've cleaned all that gunge from around the lugs, examine the state of the insulation of the paxolin board with a hand lens. Sniff for burning, smoke smells, which can linger on a transformer for years. If there's no sign of a past disaster, and all the connections from the windings to the tag board look solid, it will probably be a runner.
Well, the voltage selector that came from the mains transformer has 110 or 240 and -20, -10, -5, 0, +5, +10, and +20, but I can only trace four windings. Two are obviously 110 (2x110=220), and I assume the others are 10V each, taking it up to 240, but I don't understand the +/-5V bit.
I found an old 24V battery charger in the shed, with a decent sized step-down transformer in it. I have a variac somewhere (~2.5 Amp, I think), but I should still use a fuse between the step-down transformer and the 'mains transformer', shouldn't I? in case I get the phases wrong when testyimng the primaries.
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Simple Valve Amp
