Sluckey's Dual 50 build

[Bieworm]

well I found 2 possible transformers to replace the fried one.
one is a standard standup type and the other is a toroidal type. Both list for 2204/plexi 50W.
can I go either way, or is there one that has more pro-opinions?

https://www.tube-town.net/info/datenblaetter/transformatoren/tt-maj50-pw.pdf

https://www.tube-town.net/ttstore/toroidal-135va-power-marshall-style.html

I have to pay the expenses, so I would go for the toroidal.. if you agree?

[sluckey]

I prefer the standup transformer.

[pdf64]

…
one is a standard standup type and the other is a toroidal type.
…

With the former, what’s the voltage at the typical 150mA loading?
With the latter, what’s the max current?
I wish vendors would provide proper data.
eg no load voltage, max current and regulation.
Those 3 data points would make all this a lot easier.

[Bieworm]

…
one is a standard standup type and the other is a toroidal type.
…

With the former, what’s the voltage at the typical 150mA loading?
With the latter, what’s the max current?
I wish vendors would provide proper data.
eg no load voltage, max current and regulation.
Those 3 data points would make all this a lot easier.

You're right. It bothers me too. Some vendors even only mention the type of amp the transformer is intended for.. that's it!
But by lack of more info I'm going to follow your advice and buy an PT that's sold as replacement for a 1987/2204 amp. I have a choice between the two abovementioned.  The toroidal is very well priced,  but the stand up type might be the better option?

[pdf64]

As you’ve got a cut out in the chassis, wouldn’t it be best to get a drop through / laydown style PT?
Luke at Transformer Equipment in the UK built my last transformer set to my requirements, so avoiding this nonsense. I’ll certainly use him in future.
http://www.transformerequipment.co.uk/

I suggest to take up the issue of the failed PT with TubeTown / inmadout. If you don’t ask (eg for a replacement) you don’t get 

[Bieworm]

As you’ve got a cut out in the chassis, wouldn’t it be best to get a drop through / laydown style PT?
Luke at Transformer Equipment in the UK built my last transformer set to my requirements, so avoiding this nonsense. I’ll certainly use him in future.
http://www.transformerequipment.co.uk/

I suggest to take up the issue of the failed PT with TubeTown / inmadout. If you don’t ask (eg for a replacement) you don’t get 

Thx for the advice. I emailed Tube-Town to ask if they can treat my issue correctly. Let's wait what comes out of it. If they replace the PTX I have one to build a JTM45 in the future.
In the meanwhile I'm going to order a JMP50 transformer.  I will close the cutout with a solid aluminium plate, firmly bolted to the chassis.
The toroidal has the same specs on paper than a hammond JMP50 type transformer. It's even sold as a replacement part for a plexi, so it should be fine? I'm on a budget here...
I also don't need the extra secondaries the stand up type has..

[Bieworm]

I prefer the standup transformer.

For what reason, beyond aestetics?
The 5V wiring is useless to me and the 12.6V isn't going to be used either.
Strange thing I noticed about the stand up type is the HT current.  Tube town lists it at 175mA, but on the "poor" data sheet it's 350mA.

[sluckey]

For what reason, beyond aestetics?

Easier to install. You will likely have some challenges to install that toroidal. Personally, I would keep looking for an appropriate PT. That 350mA rating seems like big time overkill. That's probably more suited to a 4 x EL34 amp.

I also though the original PT you used was a good match. I still believe the amp was played really hard.

[Bieworm]

For what reason, beyond aestetics?

Easier to install. You will likely have some challenges to install that toroidal. Personally, I would keep looking for an appropriate PT. That 350mA rating seems like big time overkill. That's probably more suited to a 4 x EL34 amp.

I also though the original PT you used was a good match. I still believe the amp was played really hard.

So you think the 150mA would be plenty for that amp?
Is it a bad idea to think about the transformer I bought for my 5F4 build? It's a transformer sold fo the high power 5E3. It has a 320-0-320 V @ 300mA primary and 5A for filaments. I know it won't get me the 460VDC for the B+ but it will get me close to 440VDC and should still be a loud amp. Or is this stupid?

[sluckey]

So you think the 150mA would be plenty for that amp?

Yes and so does Hammond. The 290GX or 290GZ (z mount) are both listed for the JCM 800 50 watt amp, rated for 690Vct @ 150mA. Do you have access to Hammond iron?

Is it a bad idea to think about the transformer I bought for my 5F4 build? It's a transformer sold fo the high power 5E3. It has a 320-0-320 V @ 300mA primary and 5A for filaments. I know it won't get me the 460VDC for the B+ but it will get me close to 440VDC and should still be a loud amp. Or is this stupid?

Seems like overkill to me but it will work. Don't expect any PT sag though.

[pdf64]

So you think the 150mA would be plenty for that amp?

Yes and so does Hammond. The 290GX or 290GZ (z mount) are both listed for the JCM 800 50 watt amp, rated for 690Vct @ 150mA...

690V@150mA is a point on the HT winding’s voltage curve. The no load voltage is 705 and the max rated current is 213mA.
The latter seems somewhat inadequate, given the IDC loading? But if Hammond are happy to stand behind it as being fit for purpose, I’m confused. I understand that it’s pretty popular to crank a Marshall 
https://www.hammfg.com/files/parts/pdf/290GX.pdf

[Bieworm]

As you’ve got a cut out in the chassis, wouldn’t it be best to get a drop through / laydown style PT?
Luke at Transformer Equipment in the UK built my last transformer set to my requirements, so avoiding this nonsense. I’ll certainly use him in future.
http://www.transformerequipment.co.uk/

I suggest to take up the issue of the failed PT with TubeTown / inmadout. If you don’t ask (eg for a replacement) you don’t get 

Thanks for the advice again.  Tube-Town is going to replace or refund the transformer,  given the fact I spent 1000nds of € there. I will go for the stand up type JMP50 transformer this time.
Any good guidelines to detect oscillation in the output? This might also be the cause of overload, no?

[Bieworm]

For what reason, beyond aestetics?

Easier to install. You will likely have some challenges to install that toroidal. Personally, I would keep looking for an appropriate PT. That 350mA rating seems like big time overkill. That's probably more suited to a 4 x EL34 amp.

I also though the original PT you used was a good match. I still believe the amp was played really hard.

Ok I finally got some useful info from the owner...he sets the gains always at max. Always MV pretty loud. 2x at practice MV at 7. This is IMHO always max volume.  I think I will have to convert it to a 100W amp... but 4 el34 will be a tight one. How about 2x 6550?

[pdf64]

Excellent, if the vendor, and hopefully the manufacturer, get to share the pain, products may get improved.
I doubt that oscillation killed the last PT, as to oscillate so heavily that the PT was being stressed, the amp would probably have sounded awful.
It seems more likely that heavy, prolonged power amp overdrive stressed a weak spot.
Though 70% rotation (?) on a typical audio taper pot is still 6dB down from max, so the power amp may not have been getting overdriven that much.
100W is quite an uprating. Did he complain that it wasn’t loud enough?
To check for oscillation / instability, a scope, sig gen and resistive and inductive loads are needed. It’s a lot to write, so I’ll pick it up later 

http://www.sluckeyamps.com/misc/Marshall_Dual_50.pdf

[sluckey]

With that playing style I would probably put that 350mA PT in and stay with 2 x EL34. And void the warranty!   

[Bieworm]

Just want him to ge happy with his amp, no matter how loud he wants to play... I was young too once.. me and my 70's hiwatt custom 100😉

[Bieworm]

I just noticed the amp was set to 8 Ohm. He's running a 16 Ohm 1960AX cab on it. This stresses things even more, no?

[Bieworm]

Got the new PT.  The JMP50 type.. should have bought it in the first place. It's much bigger. And the chart says 350mA after all.. the text on the webshop says 175mA.

[sluckey]

Looks good. Sound OK? Fingers crossed for luck.

Is that a 220K 1/2W bleeder resistor on the first filter cap? With B+ at 450V a 220K will dissipate .9 watts. I'd want at least a 2 watt resistor in that place, probably use a 3 watt.

[Bieworm]

It sounds great! Did some tweaks on the Mica cap values in the 2204 part. And put in a 12at7 in V2 to tame the gain which makesit sound more musical and reduces the ugly distortion with pre and MV maxed out.
I have the amp on ON now for half a day and imswitching it off tonight. The bulb limiter is in series with it.

The 220k is a 2W MF.  Might have a 5W somewhere...thx for the tip

[pdf64]

I just noticed the amp was set to 8 Ohm. He's running a 16 Ohm 1960AX cab on it. This stresses things even more, no?

It only stresses the screen grids and their resistors, unless a valve shorts due to that, the PT / OT current decreases.
Higher primary impedance will reduce the current that can be drawn through it.
With regard to the new PT, it kinda looks as if each lamination is bigger, but there’s less of them, ie a thinner stack.
Does they weigh much different on the scales?

[Bieworm]

I just noticed the amp was set to 8 Ohm. He's running a 16 Ohm 1960AX cab on it. This stresses things even more, no?

It only stresses the screen grids and their resistors, unless a valve shorts due to that, the PT / OT current decreases.
Higher primary impedance will reduce the current that can be drawn through it.
With regard to the new PT, it kinda looks as if each lamination is bigger, but there’s less of them, ie a thinner stack.
Does they weigh much different on the scales?

The new one is already built in. But I can tell you that the difference in weight is very much noticeable.  When the package arrived I honestly thought that they mistakeably put 2 transformers inside the box 😄😄😄

[Bieworm]

Here's the 2204 tone with a JAN Philips 5751 in V2 position. Very nice tone!!!
https://www.dropbox.com/s/bhda73n2b15kio4/jmp50%20with%205751%20v2.m4a?dl=0

[sluckey]

Nice! Makes me want to tease my hair and buy some hair spray.   

[Bieworm]

Nice! Makes me want to tease my hair and buy some hair spray.   

It's not my thang though..I'm a lo-gainer myself. But the owner plays lead guitar in an AC/DC tribune band...
That 6G3 is more my kind of amp. Wish it was a little bit louder, but it is ok...