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Power tubes to match Chicago power transformer PSC-165 and SC AP-50 Chasis

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Posted on January 3, 2017 at 00:56:57
hkyak@cycu.edu.tw
Audiophile

Posts: 10
Joined: December 26, 2011



Happy New Year You All,

About 12 years ago I was buying some Stromberg Carlson amps, and accumulated three AP-55 amps and one AP-50 amp to make two mono pairs. In the course I ended up with an almost empty AP-50 chassis. About that time I also ended up with a Chicago power tranny PSC-165 that weighs 12 lbs but puts out only 880 vct @ 165mA, 5v @ 3 A, and 4 various 6.3 V taps that total about 14 A.

Recently I have been thinking of converting the mono AP-50 chassis into a stereo amp by utilizing the Chicago PSC-165 to supply all the power. I was told by my technician that 165 mA is not quite enough to run four powerful power tubes. So I thought I design the amp to be a class A single ended instead. So here's what I plan to do:

5V @ 3A will be for 1 5U4 rectifier.
6.3 V @ 14 A should be plentiful for 2 power tubes and driver tubes.
880 Vct @ 165 mA should be adequate for a pair of Sovtek 5881 (VTL branded, I have quite a few of them) or a pair of 6L6GC running single ended. That should put out about 6.5 W in pentode mode.

I would also like to build in a couple of OD3 voltage stabilizer since I also have quite a few of them around.

I am hoping that some knowledgeable and experienced folks here can shed some light for me on the whole matter here since I am not well versed in electronics at all, although I love vintage tube equipment and own plenty of them.

Happy New Year to you all!

Hans

 

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RE: Power tubes to match Chicago power transformer PSC-165 and SC AP-50 Chasis, posted on January 3, 2017 at 09:20:42
Eli Duttman
Audiophile

Posts: 10455
Location: Monroe Township, NJ
Joined: March 31, 2000






I don't know where you got 165 mA. from. The AP-55 schematic shows 3X 5Y3 rectifiers (good for up to 375 mA.) and 4X 6L6s.

If that's not a S/C trafo and 165 mA. is correct, is that the available B+, with cap. I/P filtration? Should that be the case, choke I/P filtration yields about twice as much. SS rectification would get an approx. 400 V. rail. Voltage multiplying the 5 VAC winding would yield an O/P tube bias supply.




Eli D.

 

RE: Power tubes to match Chicago power transformer PSC-165 and SC AP-50 Chasis, posted on January 3, 2017 at 18:08:54
hkyak@cycu.edu.tw
Audiophile

Posts: 10
Joined: December 26, 2011
 Thanks very much for your reply, Eli. The trafo is not the stock SC trafo. I bought it over Epay quite some time ago but never found a use for it, and so I thought this time I put it to some good use.

The 880 vct @ 165 mA info. comes from a 1963 Chicago transformer catalog.
And I figure 165 mA should be adequate to power two Sovtek 5881 which draws about 50-60 mA each running at about 350-400V.

 

RE: Power tubes to match Chicago power transformer PSC-165 and SC AP-50 Chasis, posted on January 3, 2017 at 19:40:35
Eli Duttman
Audiophile

Posts: 10455
Location: Monroe Township, NJ
Joined: March 31, 2000
 That 165 mA. is for a tube regulated supply, presumably with a cap. I/P filter. Some info. I scrounged off the WWW shows a 430 V. rail, which confirms the cap. I/P idea.

Can you "breadboard" a SS rectified choke I/P filter PSU and see how much current you can draw, before the trafo becomes too hot to touch? Pulling something like 300 mA. would not be surprising. To protect the SS diodes against inductive kick back spikes, use a HIGH WVDC 0.01 μF. cap. in what would be the I/P position of a CLC filter. Series wired pairs of UF5408s will provide the necessary PIV capability and the 3 A. capability should be highly "idiot resistant".


Eli D.

 

RE: Power tubes to match Chicago power transformer PSC-165 and SC AP-50 Chasis, posted on January 5, 2017 at 01:46:04
hkyak@cycu.edu.tw
Audiophile

Posts: 10
Joined: December 26, 2011
 You are right, Eli. The specs are for regulated supply as per the catalog. I would do what you suggested if I could but unfortunately I am electronically inept to perform what you suggested. I love vintage tube stuff and own plenty of Stromberg Carlson, Ampex, Heathkit, Dynaco preamps and amps, but am not capable of reading or repairing electronic circuits. Hence I rely heavily on my tech for designing, building, and fixing them. I do, however, design and build my own loudspeakers as a hobby (with help from carpenters to cut the wood).

The reason I ask for advice on this project is I want to begin to learn simple tube amp design, starting from single-ended class A. And I thought I'd start from what I have at hand. What I don't have now is a pair of OPT, and once I decide on what tubes to use I can go ahead and order them.

I guess my question is, do you think my design reasonable and feasible?

 

RE: Power tubes to match Chicago power transformer PSC-165 and SC AP-50 Chasis, posted on January 5, 2017 at 02:41:40
hkyak@cycu.edu.tw
Audiophile

Posts: 10
Joined: December 26, 2011
 I should probably mention that I have a pair of Stromberg Carlson AR-432 mono integrated amps that have 5U4 rectfiers and push-pull 7027s that were rated at 30 watts. I am using 6L6GCs instead of the 7027s and they sound very good to my ears. That is the reason I want to try 6L6GC in single ended pentode mode. The Sovtek 5881s are rumoured to be quite close to 6l6GCs, being able to run safely at about 500V and dissipate about 26W max. Besides the 20ish Sovtek 5881s, I also have a pair of spare 6l6GCs, my thinking is I will design the amp with the 5881s specs so I can roll in the 6L6GCs for comparison.

 

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