WHAT CAN I USE THIS FOR?

[Marcomel79]

Hello everyone, i just got hold of this beast of a power transformer and was wondering what kind of circuit it can be used for.
Secondaries are: 5.3VAC, 6.5VAC
and HT 400-0-400. Is there a way to make it work for a JTM45? I know the PT for a JTM45 has 350-0-350 HT, but is there a way to drop the voltage?

 

[PelliX]

A paperweight, a doorstopper, a (quite formiddable) projectile(!), a nutcracker, target practice...

A hotrod pseudo Bassman?

 

[Resident 217]

High power tweed twin?

 

[Marcomel79]

a (quite formiddable) projectile(!)

Take this, neighbour!

 

[Gene Ballzz]

@Marcomel79
Current ratings might help the consensus from the peanut gallery?
Just Askin'
Gene

 

[Marcomel79]

@Marcomel79
Current ratings might help the consensus from the peanut gallery?
Just Askin'
Gene

Very good question @Gene Ballzz. The tube lineup is the following:
5U4
6Y6
6Y6
6SL7
6SN7
VR150
6AC7.
Hopefully this helps a bit

 

[Pete Farrington]

It muddies the water somewhat, 6Y6 are an audio power output valve with a 200V limit on anode voltage

 

[Marcomel79]

It muddies the water somewhat, 6Y6 are an audio power output valve with a 200V limit on anode voltage

Heres a picture of the chassis, if it maybe helps a bit....


Should be able to deliver 150mA on the high voltage...

 

[Marcomel79]

@neikeel, do you have any aces up your sleeve regarding this matter?

 

[mickeydg5]

I am agreeing with @Pete Farrington with use of 6Y6 power tubes.
That is the reason for the regulator tube, VR150, I would imagine.

Paint over them tube designations and make it a hot rod 100 watter.

 

[Marcomel79]

I am agreeing with @Pete Farrington with use of 6Y6 power tubes.
That is the reason for the regulator tube, VR150, I would imagine.

Paint over them tube designations and make it a hot rod 100 watter.

I dont want to use any of those tubes, i just wonder if i can drop some voltage to use it for a jtm45. Or maybe a 2204 circuit....

The picture of the chassis for just to guesstimate the HT current from the tube lineup

 

[Mike_LA]

O.N.M.

 

[Pete Farrington]

If you’re prepared to take a chance with it, maybe a higher voltage JTM45 kinda thing, with KT88?
A 784-103 OT should limit the current, just in case, and I doubt youd get more than 50W, so it should cope with the power.
It may be a pain with every HT cap needing to be a stacked pair, to accommodate >500V. Unless you can source 600V caps?

 

[Marcomel79]

If you’re prepared to take a chance with it, maybe a higher voltage JTM45 kinda thing, with KT88?
A 784-103 OT should limit the current, just in case, and I doubt youd get more than 50W, so it should cope with the power.
It may be a pain with every HT cap needing to be a stacked pair, to accommodate >500V. Unless you can source 600V caps?

Was the 784-103 a 8K ohm primary? I doubt ill get hold of one but Modulus has an output transformer which is based on the RS transformer used on early jtm45s. It does state that is rated for max 30 watts, so it might not be the right candidate?

 

[neikeel]

I would go two ways either a 784-139 OT and a pair of KT88 or a 1202-84 (or similar high Z OT and a quad of KT66s for a 45/100.
To use that chassis I think the twin KT88 75w (like a Park 75) would have lots going for it.

 

[Pete Farrington]

Was the 784-103 a 8K ohm primary?

Yes, my thinking is that 8k (2k class B loadline) will prevent excessive current being drawn from the PT.
Hammond sell a 7k3 OT for JTM45 https://www.hammfg.com/files/parts/pdf/1750Q.pdf

 

[playloud]

400-0-400 could be perfect for a 45/100, if current rating is sufficient (probably) and you have power tubes that can withstand the voltage (expensive if not!)

If you have a massive choke lying around, you could attempt a choke input filter. That will give you a B+ of around 0.9*400 ~ 360V. Too low for a JTM45, unfortunately.

 

[Marcomel79]

Was hoping to build a straight up jtm45 next, but i do have a quad of KT66. Now you guys got me thinking. Thank you for the help @PelliX , @Pete Farrington, @playloud and @neikeel.

 

[mickeydg5]

Do not forget zener diodes or voltage divider circuits.

 

[Marcomel79]

I think ill save this PT for a Park 75 as suggested by @neikeel, as im gonna have to build a 100W @JohnH attenuator to be able to play it....