In Search of OT for 60's SANO Guitar Amp

[zozoe]

Greetings..... I contacted Hammond & purchased a 1750Q tranny, which they recommended, but is about 4 times the size of the one I blew, & a out 10 times heavier. It simply won't fit, & my intuition tells me there's some other quality tranny that'll suit my needs. Mercury wants $350 to rebuild it, but they have a less expensive True-Tone version I'm waiting to hear back on.
Please see attachments for my required specs. Running a pair of 7591's, tranny labeled 45w, 9000 ohm CT, & 4/8/16 out.
thanks in advance for any leads!!

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[Helmholtz]

This OT certainly doesn't look like 45W.
The 7591 datasheet specifies an output of 28W with an Raa of 9K.

[zozoe]

Thanks Helmholtz,,, is it safe to use a tranny with a CT of 6.6k ohms, & a wattage of 20 or 25 watts, like a Hammond 1760H?
Thnx ॐ

[Helmholtz]

is it safe to use a tranny with a CT of 6.6k ohms, & a wattage of 20 or 25 watts, like a Hammond 1760H?

While the 7591s can be used with a 6.6k OT, the lower impedance will actually increase power output.
So the OT should be rated for at least 40W.
https://shop.ehx.com/catalog/addimages/7591.pdf

Do you have the schematic?

[zozoe]

Sorry, no known schematic except for this one that has a 5U4, instead of the 5Y3 that the amp came with. It's the only schematic to pop up when i searched for "DUAL Channel Amplifier". If I had taken a peek at the chassis, I would've seen that it was labeled 5Y3.... Hence, that's the reason I swapped in the 5U4,,, My BAD~

Again, not being terribly tech savvy, I can't say with certainty that this IS or is NOT the proper layout,, except for the 5U4, which was my bad move....

So, still dazed & confused, I'd like to stick with the same 'proper' tranny, & not adding or retracting the power output,,,
I want the amp as it was before my fateful blunder...

Could anyone kindly steer me towards the closest value tranny from Hawke, Hammond, or even Mercury Mags, who wants $350 to rebuild my bad tranny, but might have a less pricey new one... I'm waiting to hear back from them.
Please...... and thanks in advance!! ॐ

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[B Ingram]

... tranny labeled 45w, 9000 ohm CT ...

... is it safe to use a tranny with a CT of 6.6k ohms ...

... not being terribly tech savvy ... I'd like to stick with the same 'proper' tranny, & not adding or retracting the power output ...

Okay, why are we replacing the output transformer? Is it blown?

How did you obtain the specs for the output transformer if you have no schematic? Are they written on the transformer? If so, could you upload a photo of that? I'm asking to determine whether "9kΩ" was the actual impedance pop the original OT, or if it was just a guess (and now we're married to a prior-guess).

If you hadn't said you're "not technical" I would recommend removing the output tubes, applying heater voltage to the primary, and measuring the voltage developed on the secondary. Then you would get the Volts Ratio of the transformer, which is the Turns Ratio. Square the Turns Ratio and you obtain the Impedance Ratio of the transformer, and can figure out what primary impedance is present for a given speaker load.

[zozoe]

The amp turns on, proven tubes all light up. After I smoked something, and returned back to the required 5Y3.
Initially, after turning it on, there was a loud midrange noise,,, & the 7591's & especially the 5Y3, got scorching hot rather quickly.... no red-plating going on... Fast forward, now I turn the amp on & it's dead silent and no signal passes to the speaker...I'm going to again bring it to my tech, leave it with him to perform the OT checks listed in prior response....
I look at Hawkeb & Hammond & I see several that look the part, 2 wires on one side both seemingly going to ground...
The other side has 3 wires with the red one clipped & going nowhere, while the other are going to the 7591's. Mercury Magnetics is more than 4 months out for new & rebuilds.
If the 7591 pair can generate 26w, should a new tranny read as close to 26w or is it OK to go slightly higher or lower with no consequence? I don't want the amp to be any louder than it was before, & if it was a touch lower, that would be fine!!
FWIW, the seemingly unused or rashed tranny holes on the chassis are 2" apart in a perfect square, butcthe tranny that's in there, is mounted diagonally, with holes a touch over 3" apart. It's a rather small OT & this amp rocked,putting to shame most of my $2k+ boutique amps. I'll keep you all in the loop,, but I'm really eager to get it back to the way it was.
Thanks for furthur indulging me & my woes...
Kenny ॐ

[nuke]

I think the Hammond replacement output transfomer for the Blues Junior would be a decent fit and reasonably close electrically. They offer it with just 8-ohm output (1750F) or 4-8-16 ohm output (1760F).

[Stevem]

What was the basic reason for probing around in this amp anyway, did it come into your possession with a problem?

I as ask this because it seems every other month your posting on here with a different amp that you want to mod or now has a problem from you probing around in it, yet in most of your post you state that your not technically savvy and as you state in this post “ now this amp will need to go to your Tech you use”

Note I am not picking on you, but something strange is going on.

In look back thru your post from now back to last May you have posted about at least 5 different amps you have had in your hands or in your possession, what gives with this?

If you want to learn then I suggest building a small 3 tube SE amp from scratch, ( bare chassis ) and learn how to confirm that each stage and section is working as needed, and you do not even need a O-scope to do this, just a simple audio generator.

[zozoe]

Greetings, I'm still in dire need of an OT to replace the stock 'EP-3037' that's blown. The amp sounded fantastic & rockin' until I stupidly changed the rectifier from the required 5Y3 to a 5U4. Just after turning the amp on, the amp went dead,,, power was still on, but no sound.
And, there was a small puff of light smoke upon turn-on. It's a 1x12, pushed by 2-7591's & a 5Y3. I tried a full different set of tubes, and nothing. Does what happened to the OT really point to the rectifier swap, or what?
I'm not a technician, but my tech told me the OT was shot, but for some reason, I have my doubts. Thanks in advance for any & all assistance. Any particular HAMMOND tranny fit the bill? I MUST revive this amp as best as I can.....
Kenny ॐ TY StevenM for you patience & kind expertise!!

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[Helmholtz]

Still not clear if the OT is actually bad.
It's unlikely that the 5U4 would have damaged it.
Do you have B+ with the 5Y3?

[zozoe]

I'll check,,, Back to my tech with a sledgehammer
thnx

[Stevem]

Put the 5Y3 back in and I bet the amp works again!

You also need to note that the filaments in a 5U4 need 1 more amp of current over the 5Y3.
I doubt the amps power transformer has anywhere near that extra current to dispense.

In a way your lucky if it turns out that the 5U4 was bad because if it worked you would have burned up the amps power transformer or in the least blown the mains fuse, or perhaps both.

[solderhead]

Without some data to work with, the best that anyone can do is to guess about the nature of your problem.
Please mark-up the schematic with a map of the amp's AC and DC voltages.

[zozoe]

Thnx, but unfortunately there are no known schematics for much of the Sano roster......