WTB: B&W 51SB-B Audio Transformer

[Gene Marcus]

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?

Thanks in advance.

Gene W3PM
gmarcus (at) knology (dot) net

[Scott Dorsey]

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


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

[Gene Marcus]

> 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

[Scott Dorsey]

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."

[Scott Dorsey]

>>>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."

[Michael Black]

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

[Gene Marcus]

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

[Edward Knobloch]

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
>

Hi,

Looking at the 51SB schematic, is the T-201 input transformer
for the antivox circuit the same as one you need?
If so, move that transformer over and use any generic
20,000 Ohm to 600 Ohm transformer for the antivox input.
(You don't need precisely 500 Ohms in the antivox circuit).
The antivox input circuit has no d.c. current at all
in the high Z winding, so any small transformer
will work there.

73,
Ed Knobloch

[Gene Marcus]

Edward Knobloch wrote:

> 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
>>
>
> Hi,
>
> Looking at the 51SB schematic, is the T-201 input transformer
> for the antivox circuit the same as one you need?
> If so, move that transformer over and use any generic
> 20,000 Ohm to 600 Ohm transformer for the antivox input.
> (You don't need precisely 500 Ohms in the antivox circuit).
> The antivox input circuit has no d.c. current at all
> in the high Z winding, so any small transformer
> will work there.
>
> 73,
> Ed Knobloch

Thanks for the tip Ed, but I have used T-201 to replace T-204 in the
past. T-202 is bad. When all is said and done, I will probably have to
use the two good original transformers as a matched pair in the output
circuit (T-202 and T-203) to maintain balance.

I don't know why the audio transformers seem to be the weak link in
this rig. The B+ is correct and I'm measuring 4 ma through the
high Z winding, well below the rated 10 ma.

73,

Gene

[Edward Knobloch]

>> 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
>>>
>>
>> Hi,
>>
>> Looking at the 51SB schematic, is the T-201 input transformer
>> for the antivox circuit the same as one you need?
>> If so, move that transformer over and use any generic
>> 20,000 Ohm to 600 Ohm transformer for the antivox input.
<snip>
>> Ed Knobloch
>>
>> Gene Marcus wrote:>
> Thanks for the tip Ed, but I have used T-201 to replace T-204 in the
> past. T-202 is bad. When all is said and done, I will probably have to
> use the two good original transformers as a matched pair in the output
> circuit (T-202 and T-203) to maintain balance.
>
> I don't know why the audio transformers seem to be the weak link in
> this rig. The B+ is correct and I'm measuring 4 ma through the
> high Z winding, well below the rated 10 ma.
>
Hi,

Gene, you might consider picking up a Heath SB-10 sideband adapter.
It is a near clone of the B&W 51SB, and should provide the transformers
that you need inexpensively.

73,
Ed Knobloch

[Scott Dorsey]

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."

[Scott Dorsey]

Gene Marcus > wrote:
>Thanks for the tip Ed, but I have used T-201 to replace T-204 in the
>past. T-202 is bad. When all is said and done, I will probably have to
>use the two good original transformers as a matched pair in the output
>circuit (T-202 and T-203) to maintain balance.

Sowter 9915. Freaking expensive but it's what you want.
http://homepages.tcp.co.uk/~sowter/acatalog/SOWTER_PRO_VINTAGE_TRANSFORMERS_5.html

I am really, really surprised Hammond doesn't still make one.

>I don't know why the audio transformers seem to be the weak link in
>this rig. The B+ is correct and I'm measuring 4 ma through the
>high Z winding, well below the rated 10 ma.

Probably because they got the cheapest possible transformers from a low
bidder, since they were commodity items. And they have a huge number of
turns of tiny wire in the primary, so it doesn't take much to damage one.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Gene Marcus]

Scott Dorsey wrote:

>
>
> Sowter 9915. Freaking expensive but it's what you want.
> http://homepages.tcp.co.uk/~sowter/acatalog/SOWTER_PRO_VINTAGE_TRANSFORMERS_5.html
>

Wow, your not kidding. I think this project will be on hold until I can
either find a replacement or a junk donor rig at a hamfest.

Thanks for all the info Scott.

Gene

[Scott Dorsey]

Gene Marcus > wrote:
>
>Wow, your not kidding. I think this project will be on hold until I can
>either find a replacement or a junk donor rig at a hamfest.

Whenever you go to hamfests, ALWAYS go through transformer boxes. Anything
you see for a couple bucks, buy it. Sooner or later you'll need them all.
--scott

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