Identify small power transformer based on numbers stamped on top

[jmccanna]

Hi,

I hope you are all safe and staying hunkered down.

I am considering changing out a small transformer on a Bogen preamp I scored in a trade.  The existing transformer, by design, maxes out at 125 B+.  Testing after warmup shows it putting out only 110 v.  I am thinking I could just increase the output by replacing the transformer with double the voltage and make adjustments to the other components downstream.  I know this transformer puts out B+ and heater voltage.  I have attached the schematic.

I plugged in the numbers stamped on it into Google and got no useable information.  It is probably me not asking the right question.  The numbers are:

83-538-000-6 and just below that number:
798 6112

Is there a repository I can search to identify the existing transformer?

Thanks in advance.

[jmccanna]

To save everyone time, I did not know that the codes were called EIA codes. I am first going to do my due diligence and search for that information.

[JayCobie]

Well, I can atleast say that the 798 is the EIA production source code for the "Supreme Transformer Company" which, according to my limited records, was atleast active between 1953 and 1989

6112 indicates that it was made in the 12th week of 1961

Cant help you more with the part itself though.

If you're ever in need of EIA codes, i made a freely available spreadsheet from every EIA code list I could scrape together:
https://docs.google.com/spreadsheets/d/1P1jeVIQ9UdwlhXTDLQEDxYuShjFQZO_4tUchw5_8N9o/

[jmccanna]

Hi,

I just found this list prior to your posting.  Thanks for the link though.

[PRR]

> I am thinking I could just increase the output

WTH does it need "more output"? It outputs a line level. If severely flogged it could make 10V audio output into 100k load, 5V in 10k load. Line Inputs rarely need over 2V of audio signal.

Do you mean "more gain"? Gain does not need high B+. This thing can make 2V output with 0.013V input, a soft strum. If you only want one input there is more possible, but 13mV is already way-low, close to universal hiss.

Do you want "more Distortion"? For that you REDUCE the B+.

[jmccanna]

PRR - you are correct. I made a poor choice of wording and mixed it up.  I want to decrease distortion by increasing the voltage (I said output incorrectly).

Since the voltage at the plate is low, the preamp distorts too easily - at least - I believe that is why. I liken it to those starved voltage distortion preamps that are out there. So, I wish to raise the plate voltage to increase headroom before distortion and make adjustments to control gain otherwise.

I am no electronics genius - fairly obvious I am sure - but will be looking at a way to insert a voltage doubler perhaps.  I measured the voltage off of the transformer and it is only running 110v where the schematic calls for 125v and the plate voltage was only 75v.  I believe the selenium rectifier - which is 64 years old - is a bit tired as well.  I will replace it with an 1n4007 diode.

Hope that makes sense. Stay safe all.

[PRR]

Replace the Se rectifier on general prejudice. That may get more-like plan voltage.

But 125V-110V is not a big deal. All tube-work is +/-20%.

A doubler, if possible(*), would suck FOUR times the power, on a PT which is clearly penny-pinched to the bone. Note that the 100VAC and the 6VAC are on the "same" winding. Saves a wire. Doesn't save much cost. The fact they did that "special" suggests it may only be sized for 100V*4mA and not 200V*8mA. Sucking another Watt *may* let the smoke out.

(*)The rectified B+ returns in the two 47 Ohm heater-balance resistors. Or maybe mostly in one of them since it is half-wave. I have never seen that. I'd have to try to start to understand. I'd think that any doubler would induce massive buzz in heater lines.

Anyway if this thing really distorts at Line Level, something is not as Bogen made it. It should accept any crystal or dynamic mike, or all but the hottest g-pickups, cleanly (<1%THD). It is never going to drive a speaker, not even a headphone. 

If you need it to eat HOT guitar, replace all the wiring to R7 C2, give each input preamp its own 2.2k cathode resistor, un-bypassed.