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Hammond OT's

DonP1

DonP1

Active Member
I have a pair of Hammond OT's I bought new many years ago (late 90s) still in the boxes. I'm trying to figure out if anyone has used these for hi-fi, or if these are better for guitar amps?

I've done some searches here but find little in the way of opinions about Hammond OTs. I'm how these would compare to Dynaco Z-565's for making a scratch build ST-35 or similar.

If these are not the greatest for hi-fi, I have an empty Marshall 2x12 cab and chassis that I could make into a stereo guitar tube amp, if these would be good for that.

If not good for either, I could start over with Heyboer or some other iron.

1608
10 watts
8,000 ct
100 ma. max DC per side
4-8-16 ohm taps
2.5 lbs

1650F
25 watts
7,600 ct
128 ma. max DC per side
4-8-16 ohm taps
4 lbs

I have this for a new power trannie.
270FX
138 VA
115 VAC
60 Hz
550V C.T. @ 173ma. RMS
5V @ 3A Filament 1
6.3V C.T. @ 5A Filament 2

Thanks.
 
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Hammond are quite good - better than Edcor for example, but perhaps not quite as good as Dynaco. I used a pair of 1650N to build a hifi amplifier back in the 90s, and it still sounds good today - nice square waves, good performance all around.
 
Both those models you suggested (Hammond 1608 and 1650F) are okay output transformers. I've used them both myself. Hammond OPTs have a signature high frequency characteristic to them--they are all wound with the same basic approach. By the way I'm talking about the "traditional wind" secondaries. The "easy wire" secondaries have the "A" designation in the model number and I don't have any experience with those.

The traditional wind secondaries work pretty well in feedback amps that utilize the OPT secondary in the loop, as long as you don't add too much feedback. I have found best results when wiring secondary for 4/8 ohm outputs, and taking the feedback signal from the 4 ohm tap. That produces the most stable result. Their frequency response is exactly as advertised at full rated power: 30 Hz to 30 KHz. If you don't exceed approximately 12 dB feedback that includes the secondary in the loop, you will be fine. Anything above 12 dB starts to encroach on stability. To make the amp stable above approximately 12 dB feedback requires more aggressive step filters which negate the feedback at higher frequencies. Keep it to about 12 dB feedback or less and you should be fine.

The "easy wire secondaries" are a different animal, which I have no experience with.
 
Thanks for the input @maxhifi and @kward. I originally bought these when I was only into guitar amps, and maybe I should stick to that path.

How bad would it be to use the 1608 with 6V6 tubes for guitar? There is a 1609 model with 10K P to P. I'm thinking of using a pair with my PT., and it would be easier to use octal tubes.

Thanks.
 
For guitar I don’t see any problems. Same issue with amount of feedback still applies though.

Don’t get me wrong, the hifi amps I’ve built with Hammond iron sound good to very good as long as you keep within their constraints. They don’t measure as well as same amps built with better iron, such as Dynaco z565.
 
I'm pretty sure I used substantially more than 12dB of negative feedback with the 1650N, but it's been a long time, I finished that amp in 1998. I may have put a filter in, to get a high damping factor at low frequencies.

At the time I was a subscriber to the theory that you can't hear harmonics of 10kHz and above, so best to optimize for lowest mid band distortion.

The amp really does sound good though, I wouldn't hesitate use hammond for hifi .
 
That’s exactly what I had to do, meaning put a filter In to get high damping factor at low frequencies. Specifically, the last amp I built with Hammond 1650H iron I applied 18 dB feedback in the global loop that included the secondary configured for 4/8 ohm operation. To make the amp unconditionally stable under any load type at any frequency at any power output level required an aggressive step filter. Oh it worked and was unconditionally stable, but HF response and distortion figures were more what you’d see under open loop conditions. The downhill slide on HF response started at about 12 dB.

Still that amp sounds quite good with a nice sweet presentation to it. The owner is very happy with it.
 
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