Drawmer S3 Compressor Out Transformer Help
« on: March 30, 2021, 10:14:12 AM »
A compressor Drawmer S3 with an output transformer in bad condition (an open wire) has arrived on my workbench.
Unfortunately, the manufacturer Drawmer is out of stock.
The output stage is a tube 12BHT.
Any suggestions to replace this transformer?
Thanks




Re: Drawmer S3 Compressor Out Transformer Help
« Reply #1 on: March 30, 2021, 10:30:01 AM »
The output section is somewhat similar to this drawing. There are about 200 volts at the center point of the transformer.

gyraf

Re: Drawmer S3 Compressor Out Transformer Help
« Reply #2 on: March 31, 2021, 05:52:39 AM »
Are any feedback-windings used?

If not, just go with a 4:1 or so.. try what you have at hand in that range..?

/Jakob E.
..note to self: don't let Harman run your company..

CJ

Re: Drawmer S3 Compressor Out Transformer Help
« Reply #3 on: April 01, 2021, 01:10:23 PM »
make sure the transformer can handle about 20 ma,

#37 wire will handle 20 ma easily, but you need a lot of turns, which means a bigger core to make it all fit,

what is plate to plate resistance? no spec for that as those tubes were used single ended, 5 k is about the SE resistance,

so figure 10 to 20 k for push pull,

if you run ten times inductive reactance for good bass, then you want a pri z of about 100 K, which means pri ind = 100k/(2 pi freq)

use 20 hz, L = 100,000/(6.28 x 20 hz) = about 800 Henries pri ind.

measure the core stack of the transformer, i bet it is about 5/8" or 3/4",  so try to find something with a 3/4" stack and 800 Henries pri ind.


If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

Re: Drawmer S3 Compressor Out Transformer Help
« Reply #4 on: April 02, 2021, 06:00:12 PM »
A local vendor has a pair of Lundahl LL1689 in stock
Can it be valid here?


 

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