Gene Marcus wrote:

I am repairing my B&W 51SB-B Single Sideband Generator and need the
following audio transformer:

Primary 20,000 ohms single plate 10MA DC
Secondary 500 ohms
B&W part # T-826

Does anyone have this or an equivent substitute that you want to sell?


Is the original transformer missing, or just bad?

There are no taps in it, right?

What kind of power level are you talking about here?
--scott



Scott,

The original transformer is still there, but the primary is open.

Yes, there are no taps on it.

The primary winding DC resistance on one of the other identical good
transformers measures 870 ohms. With a primary rating of 10MA it is a
low power transformer measuring 2 x 1.5 x 1.25 inches.

Thanks for your interest.

Gene W3PM

Gene Marcus wrote:

The original transformer is still there, but the primary is open.

That's harder to fix yourself than the secondary, unless the open is
right at the end of the wind in the lead-in wires. But you CAN rewind
it by hand on the bench if you're patient, or you can pay Peter Dahl
company to do it for you.

The primary winding DC resistance on one of the other identical good
transformers measures 870 ohms. With a primary rating of 10MA it is a
low power transformer measuring 2 x 1.5 x 1.25 inches.

Any idea what the actual impedances and ratios are? If you put 6VAC
into the primary of a good one, what do you get out the secondary?

It should be no problem to use an off-the-shelf Triad output transformer
IF the ratio is close to that of a standard transformer. The real problem
is that 10MA DC-leakage thing, but that's not insurmountable.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Primary 20,000 ohms single plate 10MA DC
Secondary 500 ohms

Ahh, wait, you DID give impedances!

What you want is a 20K to 600 ohm line output transformer. I bet a nickel
Hammond makes one.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Scott Dorsey ) writes:
Primary 20,000 ohms single plate 10MA DC
Secondary 500 ohms

Ahh, wait, you DID give impedances!

What you want is a 20K to 600 ohm line output transformer. I bet a nickel
Hammond makes one.

There was a time when everyone made them. If you were making a phasing
rig, you'd need those to interface with the B&W phasing network (the
ones that came in a package like a metal tube). The B&W seemed to
be the most common, but I think the other similar networks (Central
Electronics was another manufacturer) used the same sorts of transformers.

So look for a phasing rig, and the transformers will follow.

Michael VE2BVW

Michael Black wrote:
Scott Dorsey ) writes:

Primary 20,000 ohms single plate 10MA DC
Secondary 500 ohms

Ahh, wait, you DID give impedances!

What you want is a 20K to 600 ohm line output transformer. I bet a nickel
Hammond makes one.


There was a time when everyone made them. If you were making a phasing
rig, you'd need those to interface with the B&W phasing network (the
ones that came in a package like a metal tube). The B&W seemed to
be the most common, but I think the other similar networks (Central
Electronics was another manufacturer) used the same sorts of transformers.

So look for a phasing rig, and the transformers will follow.

Michael VE2BVW


Michael and Scott,

Thanks for the tips. I did check Hammond and did not find anything
suitable. The 51SB-B does use the B&W Model 350 (2Q4) audio phase shift
network. I suppose my best bet will be to look for a junk phasing rig
at a hamfest.

Gene W3PM

Michael Black wrote:
Scott Dorsey ) writes:
Primary 20,000 ohms single plate 10MA DC
Secondary 500 ohms

Ahh, wait, you DID give impedances!

What you want is a 20K to 600 ohm line output transformer. I bet a nickel
Hammond makes one.

There was a time when everyone made them. If you were making a phasing
rig, you'd need those to interface with the B&W phasing network (the
ones that came in a package like a metal tube). The B&W seemed to
be the most common, but I think the other similar networks (Central
Electronics was another manufacturer) used the same sorts of transformers.

You saw transformers like this in most audio equipment... you'd see a
single-ended output stage, often a 6AQ5 or even a 6V6, driving an output
transformer for a 600 ohm output. This was one of the most common
transformer types around because everyone used them for their output
stages.

But you're right... Hammond doesn't have anything in the catalogue,
although they do have a 20k to 32ohm output transformer.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."