Looking for info on Hammond 1618 OT

[Iplayloud]

I have an old Riviera/Pepco amp

These were made in the late 60's from what I read. My first concern is that people say they were all originally stocked with 6v6 but mine has a pair of 6L6 and the OT looks fairly larger than the 3-4 other ones I've seen. Is it possible to confirm if that OT was designed for 6v6 or 6L6 by looking up the model number? (1618)

Also when I lookup deluxe or super reverb transformer specs I see 4.2k and 6.6k. Is this the resistance of the primary, can I measure it on my amp and draw any conclusion? The size difference makes me think it may have been changed along the way or may have been a special run. The amp has a half-tail PI so would only be around 22 watts, in the attached picture i put a Princeton OT which also has a half-tail PI with a pair of 6v6 and you can tell it's way smaller.

I am technically a semi-beginner. Thx for any help

[Iplayloud]

I sound like I'm trying to convice myself haha but I'm really just looking to put what "should" be in there.
I was thinking too if the PT was seeing twice 900 mA on the heaters instead of twice 450 mA for 6V6 it would probably overheat but not the case, it barely warms up after 30 minutes. I wrote this under this section as I'm going to have a few more questions as we go. Thx

[loudthud]

My data for the 1618 from 1948 says it's rated at 15 Watts with 10KCT primary with secondary taps for 3.2, 6.4 and 10 ohms.

[Iplayloud]

Wow fantastic! I wasn't finding any specs on Google. Will be stuffing 6V6's in there. Thx

[Iplayloud]

I saw the extra ohm taps tucked under. Is Hammond consistent with their wire colors? I looked up a couple diagrams and they were different. I think I may have to test the OT with a small AC voltage to figure which tap is which..

[loudthud]

There is no info in the catalog I have refering to wire colors. The low voltage AC will tell you which is which.

[audiopete]

I have one of these 725s all original and I have seen others with various cosmetics. They are basically Princetons with cathode bias. Pepcos are pretty common around me.

I would stay with 6V6s and not risk blowing your OT since its rated for 15W. Put 1K 5W resistors on each 6V6 cathode and bypass with 100uF/50V caps if you like. Stock bias is way too hot.

[Iplayloud]

Thx for all the info. Just to make sure my math is right when testing the OT taps with a small AC voltage on the primary, the tap with the highr voltage on the secondary will be the highest ohms?

Other thing, it has been converted to class AB with a bias supply, what do guys think, go back to original?

It puzzles me why hammond would make a15w OT as big as it is? If it's specs were only found in a 1948 manual, then it was probably replaced at some point with one that had been sitting on a shelf for some time..

[g1]

Just to make sure my math is right when testing the OT taps with a small AC voltage on the primary, the tap with the highr voltage on the secondary will be the highest ohms?

Yes that is correct.
As far as the size of that OT, I agree it looks larger than 15W that the old specs show.
Triodeel mentions using that OT for the Altec A-333-A here:
Acrosound,Altec, and Dynaco
That model Altec is rated for 27W, using two 6L6 at around 400V.

[Iplayloud]

For future reference if anyone pulls this thread.. I applied 6.04 VAC on the primary and the secondary reads the following:

.119
.168
.238

I think the math supports it being a 4-8-16 rather than 3.2-6.4-10 ohms.

(6.04/.119) squared x 4 = 10,304
(6.04/.168) squared x 8 = 10,340
(6.04/.238) squared x 16 = 10,304


(6.04/.119) squared x 3.2 = 8,243
(6.04/.168) squared x 6.4 = 8,272
(6.04/.238) squared x 10 = 6,440