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    the safety precautions around high voltages.

Anyone tried the Hammond 1642SE in a BIG SE amp?

I am wondering if anyone out there has used the Hammond 1642SE in a high power SE amp. Something over 60 Watts. This would be a PSE amp with 2 X 845 or 2 X 211 or an SE with an 833A. If so has anyone measured the frequency response of that amp. Are there any other SE transformers out there that could be used at the 50 to 100 watt level that costs under 250 USD.

I am looking for an output transformer that would work in an 833A SE amp at the 75 watt level or higher. I had an OPT custom made by a transformer winder, but the high frequency response was very uneven above 14 KHz, but I could get over 100 Watts down to 42Hz and 60 Watts at 30 Hz. I know my hearing is nonexistent above 14 KHz, but I want flat response out to at least 20 KHz. The amp did sound awesome, and the bass was unreal, even with my small speakers. I looked at the Electra_Print CU5KB, but they are beyond my budget. The Hammond is also about 10 pounds larger than the Electra-Print, and 8 pounds larger than my custom transformer. Weight = Bass response, and I like bass.

I am still looking for that magical amp that shakes the walls with the low end punch that my 300B PP amp has, and still retains the SE magic that my 845SE has. Maybe the SE 833A is it, I won't know until I have built it!

http://www.tubelab.com/833SE.htm
 
Back in the 70's, when I was just a young foolish pup.
During my early garage band days. I ran an ampeg SVT 300W all tube head into a 6-12" cab.

I played my old Gibson Melody Maker and eventually an SG standard into it.
Though the SVT was intended as a bass amp. I really loved the earth shaking bottom end with the guitar. One noteable pleasure was the intense presence of this amp, Its difficult to come up with a verb that actually does it justice.
I would be willing to guess that an OPT from one of those might be located thru evilbay at a reasonable cost. As I remember it must have weight in about 15 lbs!(guessing)

Another HUGE tranny that might work if it could be located would be from an old univox 1511. They hold up pumping 150W with a quad of 6550's PLUS, they are less than popular items .

Couldnt those types of trannies run in SE config?
Just A Thought
Gene
 
I too spent some time frying my ears playing a Hagstrom guitar through an SVT. It did sound cool. The early SVT's used 6146 tubes that were intended for mobile radio use. Ampeg switched to 6550's after too many SVT's erupted in flames, including one in a stadium show by the Rolling Stones. I saw an SVT catch fire, but it was because the owner tried playing it at full volume through a Traynor 8 X 10 cabinet that was meant for a 100 Watt head. When the speakers blew, the amp was running at full tilt into an open load. The output transformer, the power transformer, and all of the 6550's were fried!

I have experimented with using push - pull transformers on single ended amps, with varying results. Some just flat don't work, some work pretty good, but most will distort the bass frequencies. The ones that work will only pass about 10 to 20 % of the power that they would pass in push - pull mode. This is because a push - pull transformer was designed such that all of the magnetism created by the DC current will cancel out. A single ended transformer is designed to work with this standing DC current. This is done by placing a gap in the magnetic circuit. To offset the effects of this gap, the core is made MUCH larger. The transformer I am looking for will weigh at least 20 pounds. The Hammond weighs 28 pounds. I have tried modifying push - pull transformers for SE use by removing the laminations and reassembling them with a gap. This is not an exact science, and is not the approach I want for this amp.

It would be possible to use a push - pull transformer by using a parafeed configuration, but this requires an expensive choke that is usually matched to the output transformer.

I appreciate the thought, but I will probably try the Hammonds for this amp, I was hoping that someone out there has already done this. I will use the prototype transformer that I have to build a seriously wicked guitar amp using an 833A. Imagine a 60's vintage Fender Champ that puts out 200 Watts.
 
Did you ever try the 1642SE with the 833?

At the time I had visions of building a really big SE amp. I almost did it, but the vendor who had advertized the 1642SE on his web site for a low price refused to honor that price. In fact he wanted almost twice what he quoted on the web site. That project stalled for lack of a suitable OPT.

I have since realized that such an inefficient amplifier would not get much use since I live in a very warm climate. In fact my 845SE amp has not been turned on in at least two years.
 
The 1642SE is a rather singular monster. One could dream about pairing it up with a couple of GM70s at 900-1000V B+ (not that hard to drive). At the lower voltage, one would need A2 operation to squeeze out the last bit of juice, but w'ere no stranger to that here. Finding someone who actually stocks the 1642 is another matter, as none of my usual suspects apear to. However, if I really got serious about a project like this, I could probably find someone with a little more effort. This is one application where switching power supplies could be of use, transforming a project that would otherwise be a titanic boat anchor (or a huge separate power supply) to a couple of beefy monoblocks. It might be interesting to query Edcor to see what they would charge for a 1642-like transformer.
 
There was an article in Glass Audio a few years ago where someone used a Hammond 1650W push pull transformer, sliced a gap with a hacksaw, and used it for a 50W+ SE output. He was very precise about how he gapped it. Not necessary to take it apart, except for the end bells. A little searching would find the article.

Like this :D
 

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Hi Tubelab,

Did you ever try the 1642SE with the 833?

I am considering giving it a go and was wondering if you ever did get around to it?

Best Regards

James
Hi James
I did a amp 1642SE with 826 in Shisido style, 1.25k load for 826 was what he designed, but out-put only 8 watt, SE amp most for sound quality not for power, I use my 826 for supper high section in multi amp system
Tony Ma
 

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Hi Tony,

I was actually inspired by your postings in other threads about your 826 amplifier to build one.

Unfortunately I had a very hard time getting good 826 Valves. Of the 7 I tried I found only 1 good one.

So I have now moved on to a 833 SE, (as well as a GM70 PP!)

The Hammond's are on order so will post back when I make some progress.

Best Regards

James
 
I did a amp 1642SE with 826 in Shisido style, 1.25k load for 826 was what he designed, but out-put only 8 watt, SE amp most for sound quality not for power, I use my 826 for supper high section in multi amp system

Did you ever measure the frequency response? I posted this question about the 1642SE over 4 years ago because of my bad experiences with the 1628SE.

I got a pair of 1628SE's. Their frequency response was 6db dowm at 20KHz with a sharp notch at 28KHz. The phase shift across the high frequency end of the audio spectrum is not normal either.

I have since tried the 1628SEA and found it to be better, but still not meeting the published specs.

"Frequency response at least 20 Hz. to 20 Khz. at full rated power (+/- 1 db max., ref. 1 Khz.) "

I could consider a project using the 1642SE in the future, but not until someone has independent test data on one.
 
Did you ever measure the frequency response? I posted this question about the 1642SE over 4 years ago because of my bad experiences with the 1628SE.

I got a pair of 1628SE's. Their frequency response was 6db dowm at 20KHz with a sharp notch at 28KHz. The phase shift across the high frequency end of the audio spectrum is not normal either.

I have since tried the 1628SEA and found it to be better, but still not meeting the published specs.

"Frequency response at least 20 Hz. to 20 Khz. at full rated power (+/- 1 db max., ref. 1 Khz.) "

I could consider a project using the 1642SE in the future, but not until someone has independent test data on one.

sorry something wrong of my computer I reply again, I built that amp around 8 years ago and I don't care too much of distortion and frequency although I got things to check. mainly for the out put power, the rest by listening judge only. looking for transformer go for over 20K but the speakerwill not follow, in multi system gain control in crossover will adjust to match the others for best result
 
Did you ever measure the frequency response? I posted this question about the 1642SE over 4 years ago because of my bad experiences with the 1628SE. <snip>

I just "bite a bullet" and purchased the 1642SE. Life is not rose at all. It has a dip/resonance right at 17.4 kHz with the 8-Ohm output. The 4 and 16-ohm outputs does not have this dip but none of them better than 28kHz ... Moreover, somehow the winding ratio is totally off from spec. I will check the winding ratio again but the dip/resonance is definitely there. I am contacting Hammond Canada engineer and waiting for their feedback. Hammond in US and resale in US cannot help any technical issue.
 
Why use a SE OT at all? The "anti-triode" scheme solved this years ago.

You put the tube on one side of a P-P OT, and a high gm HV Mosfet on the other side of the OT primary. Then a CCS tail below them both. The tube gets driven by the audio, and the Mosfet gets a quasi static DC bias. The tube will generate some inadvertant DC imbalance with large signals due to its 2nd harmonic distortion, so some provision is needed to dynamically adjust (below 10 Hz audio band) the Mosfet gate bias to keep the DC in the OT in balance.

This gives twice the power output as the single tube alone would give, and the CCS tail along with the high gm Mosfet guarantee true complementary current in the opposite OT primary phase. The high gm of the Mosfet keeps the voltage on the tail constant, so the tube operates in a SE environment. (normal P-P split phase operation cancels the even harmonic distortion by dynamic (audio band) variation of the tail voltage, which is not allowed here.)
 
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I think the only high voltage high gm FET that will stand off 3KV+ is another 3-500ZG. Doubling the b+ current is also pretty impractical for an amp that will burn a kilowatt at idle. The balancing current could be from a low voltage buck regulator on another winding, or maybe the filament current.

I bought a pair of 3-500Z's 20 years ago. Maybe I'm old enough now to not kill myself hooking them up. If there are performance issues with the 1642SE, Is anyone interested in a group buy of a custom at Stangenes? Places I've worked for have gotten great service and customs from them.
 
Actually, IXYS has some 3 kV+ devices. They're even available at Digi-key, but be prepared to lay down some fairly serious coin. They come in a special package with extra creepage to the drain lead (smart).

I never thought of Stangenes as a possible vendor for an audio transformer, but they do other things that make that application look like a casual stroll in the park.

I just checked, and Ixys makes both IGBTs ans Mosfets at voltages up to 4kV - expect to pay...
 
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Yep,
You are correct. Ixys does have 4000V and 4500V MOSFETS for 40 bucks compared to a second 3-500z at 200 bucks. The thing is, if you have a second active device on the other side of the PP transformer, you might as well modulate it and have a PP amplifier. How about just a resistor on the other side to balance the field in the core?
Really, the 3KV b+ is a hassle to generate, so burning half of it to balance an ungaped transformer is a waste. Either a low voltage balancing winding or a gaped (SE) transformer will save a significant amount of power (like a kilowatt in this case).
Would the PP transformer with a constant current load on one side sound better than a SE (gaped) transformer?