How about Hammond 1760J for AC30 output transformer?

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psychepool
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How about Hammond 1760J for AC30 output transformer?

Post by psychepool »

I planed to make AC30 styled amp.
Want to make headamp type, and considered to use Hammond Transformer.
But Hammond AC30 transformers has just 8/16ohms secondary impedence.
1750V
http://www.hammondmfg.com/pdf/EDB1750V.pdf
1750T
http://www.hammondmfg.com/pdf/EDB1750T.pdf

I want 4/8/16ohm secondary, so I look around other products.
Hammond 1760J looks very simmilar with Ac30 specs.
http://www.hammondmfg.com/pdf/EDB1760J.pdf

It is Fender Pro Reverb/Vibrolux replacement.
Has 35W output/4K primary. Very simmilar with AC30.
And it has more wattage, small sized / light weighted, and even has cheaper price.(The half price!)

The price is also important thing.
But provides 4/8/16ohm tap and small size/ lightweight are more important point to me.
Because I will make it with headamp type.

What is different if I use Hammond 1760J for AC30?
I expect to It will no matter to operate but has some difference in sound and output level.

If anyone tried it, please give me advice.
Stevem
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.p

Post by Stevem »

The AC30 OT is the mass / weight that it is due to the Class A that it is, in light of this I would not go smaller!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!😊

Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
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JazzGuitarGimp
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Re: .p

Post by JazzGuitarGimp »

Stevem wrote:The AC30 OT is the mass / weight that it is due to the Class A that it is, in light of this I would not go smaller!
From Merlin Blemcowe's Valve Wizzaed website: "and no, the Vox AC15/30 are NOT Class A amps!)." Here is the link to the push pull power amp tutorial (which contains the quote above):
http://www.valvewizard.co.uk/pp.html
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Stevem
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M

Post by Stevem »

Well next time you get a AC15 or 30 on your bench measure how little the output plate current changes between idle and max output!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!😊

Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
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martin manning
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Re: M

Post by martin manning »

Stevem wrote:Well next time you get a AC15 or 30 on your bench measure how little the output plate current changes between idle and max output!
The next time you have one on your bench, scope the cathode current. To do it properly you will need to put a 1R between the cathode resistor and the cathodes on one side, and use a two channel scope with the probes on either side of the 1R. Set the display to show the difference between ch1 and ch2. As you bring the input signal up you will see the voltage go to zero for part of a cycle indicating cut-off, and proof that the power amp is Class AB.
pdf64
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Re: How about Hammond 1760J for AC30 output transformer?

Post by pdf64 »

The schematic notes that cathode current increases 25%, from idle to full power http://bmamps.com/Schematics/vox/Vox%20 ... ematic.pdf
Aiken's analysis seems to be that it's a 25 watt class A amp which has had the HT raised http://www.aikenamps.com/index.php/is-t ... ly-class-a
Whatever, as with any decent cathode biased p-p guitar amp, it necessarily runs close to class A, much higher idle current than intended for any Fender <= 50W.

The AC30 OT dwarfs that scratty Fender Pro OT, it has about as much iron as a Super Reverb OT, which (surprise surprise) costs about the same.

Regarding a 4 ohm output, note that having speakers connected in series rather than parallel (and the consequentially reduced speaker damping) may be a factor in the Vox tone character.

I seem to remember that the Pro OT is low spec, with no interleaving.
I built a Vibrolux / Pro Reverb type amp with a Mojo replacement Pro type OT and it has a great, unusual midrangey tone. But with a SR sized OT, there's noticeably more of everything, especially in regard of solid bottom end and high treble; even my drummer noticed and asked what I'd done to it!
It tested about the same on the bench though.
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rp
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Re: How about Hammond 1760J for AC30 output transformer?

Post by rp »

AC-30 is pretty unique tone, I'd stay with cloned iron. What is good iron beats me, I've never tried to clone an AC30. Here's one off the shelf option w/ 4/8/16 <http://www.classictone.net/40-18049.html>

I'm not a fan of the Mercury business model but they got their fame with vintage Marshall and Vox OT clones, and offer Parmeko, Woden, Haddon and Albion repos, have to give them credit on that. Maybe they offer a 4/8/16? Maybe Hoffman or RJ here could order you one at a better price, though that will still be a lot.

Heyboer will know how to wind an AC-30, bet they are familiar w/ the different eras too. Their up-charge for a custom with 4/8/16 will only be $20 more than retail.

If you want to deviate a bit I'd go with RJ's Pacific Rock-it OT w/ the 3.9K tap. Maybe not be 100% Vox but very likely 100% good.
Last edited by rp on Fri May 13, 2016 6:33 pm, edited 1 time in total.
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rp
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Re: How about Hammond 1760J for AC30 output transformer?

Post by rp »

Regarding a 4 ohm output, note that having speakers connected in series rather than parallel (and the consequentially reduced speaker damping) may be a factor in the Vox tone character.
!!! All these years never gave that any thought. It'll use the full winding too. Very interesting.
psychepool
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Re: How about Hammond 1760J for AC30 output transformer?

Post by psychepool »

Thanks all!

I'm not good about a circuit theory. Not major about electronics. Just make it for hobby.
(Even I'm not good at english :) )
I didn't understand you say completely, but in short that I understand is,
AC30 is just 30W but it needs very high current circuit compare with other 30W circuits.
So Hammond 1760J is not proper for AC30 output circuit.
It wouldn't be a good idea to replace the OT with fender 35W spec.


I considered to use classictone transformers for 4/18/16ohm tap but I live in South Korea. Shipping cost is very high to order.
The reason to use Hammond is shipping cost.
Mouser or Digikey deals Hammond transformers and if the price is over about 60$, they offers free shipping.


Thanks all anyway!
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Turbojunkie
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Re: How about Hammond 1760J for AC30 output transformer?

Post by Turbojunkie »

Using an open back cabinet with 2 8ohm speakers wired in series, like pdf64 mentioned, is a factor for sure, if getting the traditional/classic AC30 sound is very important to you....in which case Celestion Blues make an important contribution as well. Certainly not the only speaker configuration that sounds great, but that's the most authentic sounding setup...
Parallel wired 4 ohms is cool, a clearer & less compressed sort of thing, especially if you're using a closed back cab.
The only setup I really didn't like was running them at 16 ohms/series in a closed back...too sloppy and "confused" sounding.
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rp
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Re: How about Hammond 1760J for AC30 output transformer?

Post by rp »

These Hammonds will work much better than the 1760J. Whether they will give you that Vox sound is a risk you have to take. Certainly won’t sound bad at all.

1760L 50W Fender Bassman
1750G 50W Yorkville/ Traynor

Lot’s of sellers in Asia on eBay, lot's of HiFi. Can’t recommend personally, but here’s some ideas:

http://www.mableaudio.com/en/productvie ... ormer.html

http://www.mableaudio.com/en/productvie ... ormer.html

Any Asian clone of a Dynaco ST-70 (A470 type) will work well. A470s are proved in many TW rockets which are just AC30s. A contributor here has a site: http://www.rjguitars.net/

Any 3.8K-4.4K Asian hifi OT accurately rated @20H-20kHz at 30W will be more like >50W at 80Hz for guitar and will work.

Personally I would get the Hammond Vox 1750V (paper) and do series wiring as recommend.
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jaysg
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Re: How about Hammond 1760J for AC30 output transformer?

Post by jaysg »

If you can find a connection with an MM 25+, they're not any wor$e than any other make. If not, I would go with a Heyboer Woden OT. I don't know the number, but it's supposed to be just fine. The MM might give you better resale...dunno. Do not go with Hammond or a Fender. AC-30 iron may as well be Marshall 50W iron. Heavy suckers.

fwiw, I have A/B'd the MM Woden with the CC iron. The MM is less hifi. It makes for a more compact sound and while that may sound wrong, it's what it is and people want that.
psychepool
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Re: How about Hammond 1760J for AC30 output transformer?

Post by psychepool »

I changed my mind with you say.

The 4ohm tap wouldn't be indispensable.
Just 8/16ohm tap seems enough to use even I make it with headamp style.
It's sad to bigger and heavier than 1760J, but it seems to be a destiny to make AC30.

I still can't use except Hammond OT because of the shipping cost.
For bring it to my home, I must pay the shpping cost almost the product's cost.

I will use Mecury or Heyboer and etc if AC30 is my destiny gear. But it is not.
If someday there's my favorite gear, I will try other famous transformer.
Badside
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Re: How about Hammond 1760J for AC30 output transformer?

Post by Badside »

I was comparing the finer specs: both have the exact same inductance: 90.95H, although one is measured at 60Hz and the other at 70Hz. No idea why.

More interestingly though, the AC30 tranny (the 1750V) has a significantly lower DCR (DC resistance): 138 ohms vs 185 ohms. Given the pretty sizeable idle current an AC30 gets (somewhere between 125 and 150mA if memory serves right, basically 4 EL84s running slightly over max dissipation at around 330-340V, the thing is a tube oven), that's probably on purpose, the AC30 probably uses bigger gauge wires to waste less heat and thus ends up being bigger.

What else, the 1750V is a paper wound coil, while the 1750J is a plastic bobbin (note: the 1750T also uses a plastic bobbin).

FWIW, I have built an AC30 clone with the proper Hammond iron: 1750V output and 290MX power (the 290NX "vintage style" is a bit more complicated to mount if you don't have a proper repro chassis), it's one of the sweetest amps I've ever done.
Yes the 1750V is expensive, but it's the real deal if you want the real tone.

I too have to prioritize Hammond because anything else is twice the price after shipping and customs, never been disappointed with their guitar lines (290 PTs and 1750/1760 OTs).
Amplifiers built:
Marshall 2204 head with some mods
Low-power 2204 (cathode biased 6V6s)
Single-knob dual-6K6GT amps using a Wattkins uPCB
AC30 clone with Plexified preamp section
AX84 Firefly
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