Can JTM45/50 PT work for Ceriatone OTS FM 50?

[itsgiusto]

I'm building a Ceriatone 50 watt clone of the Dumble #102 amp.
http://www.ceriatone.com/overtone-special-fm-50/

I was planning on using this JTM45/50 PT, since it has a 5v secondary I could use to power some 3v relays:
http://www.classictone.net/40-18054.pdf

However, I just noticed that while the voltages are correct for the b+ secondary (690v), the current rating might be low, it says it's only rated at 150ma on that winding. Also is not clear if it's rated at that current for the 625v tap or the 690v tap.

Is this something to worry about? What is the current draw of this amp on that winding?

[statorvane]

The current rating is at 690 V CT. I used this PT for a JCM 800 clone for my son about 15 years ago. https://www.tubesandmore.com/products/t ... power-50-w Same power specifications, but no 5 V winding.

2XEL34s and 3x12AX7s. Still rocks.

Shouldn't be a problem. Classictone are very good transformers.

[pdf64]

The 690V @ 150mA is just a reference point. At full load, a pair of AB1 EL34 into a 3k5 load will draw over twice that from a biphase HT winding.

[Richard1001]

I don't no if it is a reference point, but you won't bridge rectify the two HV coils in series making close to 1000V right?
Rectifying the AC with the centertap to ground will put the coils in parallel and you will have halve the voltage and double the current.

[itsgiusto]

The 690V @ 150mA is just a reference point. At full load, a pair of AB1 EL34 into a 3k5 load will draw over twice that from a biphase HT winding.

Yeah, I was wondering if it was just a reference point or not. I use this same type of transformer in my Plexi build, and when I run it on full blast, it's sometimes been enough to blow the HT fuse at 500ma, so that implies that it can output 500ma sometimes. Still though, some of the other Fender-style transformers from Classictone, like the one for their Pro Reverb or Bassman are rated at 200ma or more (granted, the voltage is different), so I still wonder if this is enough. (see http://www.classictone.net/40-18073.pdf for a Fender-style transformer)

I don't no if it is a reference point, but you won't bridge rectify the two HV coils in series making close to 1000V right?
Rectifying the AC with the centertap to ground will put the coils in parallel and you will have halve the voltage and double the current.

Not sure I'm understanding. Each tap on the B+ winding is 345v ac, so when rectified and filtered, the B+ should be more like 488v dc. Of course, under load, it'll be less. On the spec sheet I posted, they say it's something like 450v @ 150ma load when used with a diode rectifier.

[Roe]

The pt will sag considerably but work

[itsgiusto]

The pt will sag considerably but work

Hmm, interesting. What effect will that have on the amp and tone?

If it has a negative effect or will significantly alter tone, do you have an alternative PT you'd recommend (without spending Mercury Magnetics cash)? I have a separate 6v transformer I could use as well, so the transformer I pick does not need to have the additional 5 or 6v winding, that's just a bonus. But I seem to have a difficult time finding a transformer that has a 690v secondary, which is what Ceriatone recommends, and I'm not sure what the current rating should be for optimal tone, avoiding sag, etc.

Update: Just messaged Nik, actually, he says that the B+ winding should be rated 150-200mA. So maybe it is enough?

[Richard1001]

The 690V @ 150mA is just a reference point. At full load, a pair of AB1 EL34 into a 3k5 load will draw over twice that from a biphase HT winding.

Yeah, I was wondering if it was just a reference point or not. I use this same type of transformer in my Plexi build, and when I run it on full blast, it's sometimes been enough to blow the HT fuse at 500ma, so that implies that it can output 500ma sometimes. Still though, some of the other Fender-style transformers from Classictone, like the one for their Pro Reverb or Bassman are rated at 200ma or more (granted, the voltage is different), so I still wonder if this is enough. (see http://www.classictone.net/40-18073.pdf for a Fender-style transformer)

I don't no if it is a reference point, but you won't bridge rectify the two HV coils in series making close to 1000V right?
Rectifying the AC with the centertap to ground will put the coils in parallel and you will have halve the voltage and double the current.

Not sure I'm understanding. Each tap on the B+ winding is 345v ac, so when rectified and filtered, the B+ should be more like 488v dc. Of course, under load, it'll be less. On the spec sheet I posted, they say it's something like 450v @ 150ma load when used with a diode rectifier.

Transformers transform the voltage and impedance but the power stay's the same. The power rating given in the data sheet is no reverence point. It shows the maximum output power of the HV winding. 690V @150 =103,5 VA of power. Maximum output power is given when the load impedance matches the transformerwinding impedance.
The winding can provide more current, connecting a lower impedance, but then the voltage would drop. With no load the voltage goes up, but there is no current flow. In both cases there is a mismatch and the transformer will not give it's maximum power.

Cutting the 690V winding in two windings of 345V, using the centertap, you have two windings with halve the impedance of the total winding is series. Both windings combined this way can provide 300ma. With each winding having 1/2 the impedance and working only 1/2 a cycle, the avarage current through each half of the winding stay's the same. So it's like putting the two windings in parallel.

On the Primary side of transformers you often see the same thing. Having two 120V windings that can be put in parallel for 120V mains and in series for 240volt. The current rating of the parallel (120v) wiring will be twice that of the series 240V wiring. Here also, the power input stay's the same.