stancor p-6157

[N8DLJ]

Just picked up a old boat anchor, circa 1950-60, amplifier. Just guessing age by the design and components used. First thing I'd like to do is find the ham that built this and shake his hand. It is a 10-15-20-40 and 80 amplifier. Looks like no expense spared, carefully built and laid out. The Power supply section needs gone through and modernized. This one has mercury vapor rectifiers and original caps. No soft start or delay timer circuits included.

Anyway, to my question. The Hv Xformer is a Stancor P-6157. 1250/1500/CT. It is currently 1/2 wave rectified and hooked to the 1500 tap. The amplifier has 4 RCA 811a finals. Seems to be a little hot for 811a's in my opinion. Thinking about putting it back together as a 572b amp. Full wave on the 1500 tap. Looking through a old Stancor catolog and online I can't find any info on the P-6157 transformer.

So a long way to a short question. Anyone have info on the Stancor P-6157?

73

[WB2WIK]

Before changing anything:

-Are you sure it's capacitor input and not choke input? It was very common in those days to use a filter choke, which would provide about 0.9 x the RMS secondary voltage and not 1.4 x. Did you power it up and actually measure the DC voltage?

-Mercury vapor rectifiers don't need any sort of "soft start" or timers.

-You said it's 1/2-wave rectified, but then also said "rectifiers." A 1/2-wave circuit would only require one rectifier, and would actually be very unusual. Are you sure about that circuit? Sure it's not a full-wave C.T. or bridge? For that kind of current demand (4 x 811As) a 1/2-wave rectifier would be unusual indeed.

Before changing anything I'd fire it up and take some measurements. Unless the caps are dried out, I'd expect it to work. If the caps are dried out, I'd expect the line fuse to blow but I wouldn't expect any other failures.

866's and similar rectifiers last forever. Remember they must be operated base down and never upside down or sideways.

[K9STH]

Also, you might have to apply only filament voltage to the 866 rectifier tubes for an hour, or so, if they haven't been in use for a while. Some people think that 24 hours is more like it.

Otherwise, you might have all sorts of "displays" if you apply HV without "seasoning" the tubes.

Glen, K9STH

[N8DLJ]

Showing my age. I'm not at all experienced with a choke input set up. Yes it is a choke set up.

As far as plugging it up, one of the rectifiers is cracked and I don't have another one. Next problem, I already started pulling it apart. Although it was modern technology back then I prefer diodes, capacitors, soft start and dummy lock out aka timer circuit. If there is anybody I know it is me. I know there are times when I can't wait for tubes to heat up, dummy lock outs are made for people like me.

Rectifier(s) wired in parallel and 1/2 wave. Unusual .

As far as burning in the tubes. The 811a's are upstairs. I have a old mobile 2 X 811a that makes a good tube tester. Got one pair burning now. The rectifers, one goes in the trash and the other goes in the tube box.

I have other amplifiers to use, most of the time they are in the off position. This one just has a vintage look and I like it. A old bud cabinet with chrome accents.

I'm just throwing ideas around in my head. A 4 x 572b isn't anything exciting but I'm not going to throw a bunch of time and trouble into going another direction. It is going to be a 811a or 572b amp. Probably just sit there and look pretty after I'm done.

But to make up my mind I need to know the actual ratings on this x-former. It is big, it is heavy but only a 115v primary.

Thanks to both of you for the suggestions. Time to head to work. 73

[WB2WIK]

Showing my age. I'm not at all experienced with a choke input set up. Yes it is a choke set up.

As far as plugging it up, one of the rectifiers is cracked and I don't have another one. Next problem, I already started pulling it apart. Although it was modern technology back then I prefer diodes, capacitors, soft start and dummy lock out aka timer circuit. If there is anybody I know it is me. I know there are times when I can't wait for tubes to heat up, dummy lock outs are made for people like me.

It's unfortunate you did that. 866As are far more robust and resilient than silicon rectifiers are, I'd have replaced them and used them. I'd leave the choke in place also, but maybe re-wire the circuit for full-wave rectification instead of half-wave, which makes almost no sense. I can't imagine why anyone would do that.

Rectifier(s) wired in parallel and 1/2 wave. Unusual .

Sure is. Makes the ripple frequency 60 Hz, much harder to filter. Something's weird, there.

As far as burning in the tubes. The 811a's are upstairs. I have a old mobile 2 X 811a that makes a good tube tester. Got one pair burning now. The rectifers, one goes in the trash and the other goes in the tube box.

Glen didn't recommend burning in the 811As. He recommended burning in the mercury vapor rectifier tubes, as if they've just been sitting a very long time this isn't a bad idea. 811As don't need any burn-in, and they also don't need any "warm up" time. They're instant-on tubes.

[WB2WIK]

BTW the P-6157 seems non-standard.

Here's the entire Stancor transformer catalog from 1961 and thousands of models are listed, but not that one:

http://www.clarisonus.com/Archives/Trans/Stancor61.pdf

[K1ZJH]

Mercury vapor rectifiers should be choke input. They will not handle the repeatitive peak charging current. That's why most of those early
amps used choke input. Many of those power transformers were rated for choke input as well.

Pete

[WB2WIK]

Mercury vapor rectifiers should be choke input. They will not handle the repeatitive peak charging current. That's why most of those early
amps used choke input. Many of those power transformers were rated for choke input as well.

Pete

I agree, and wouldn't have changed anything, especially to maintain its "classic-ness."

[KM1H]

Mercury vapor rectifiers don't need any sort of "soft start" or timers

They sure do need the above. Filaments require a minimum of 30 seconds before applying HV for the 866A and longer for bigger ones. If the choke L is marginal a step start prevents an intense voltage spike guaranteed to destroy the tube.

If the MV's have been sitting vertically with the base down for a long time a 30 minute first warm-up is fine, otherwise 2 hours or so to get the mecury into the base where it belongs. Its easily visible where the mercury is at anyway.

IMO, I dump all 866A's and use 3B28's which are a hard vacuum argon filled tube which has none of the 866A faults. Otherwise go with a string of 1N5408's as the voltage drop difference can barely be measured with either tube. There are also plug in SS replacements which show up regularly and were especially common in BC, FM and TV service in now scrapped condition, 1N2637 is probably the most common.

Carl

[KH2G]

If only the base of the 866 is cracked, the tube is probably still good. Love those old things and watching the blue glow change as you operate.