“Jtm 45” help

[Snake5150]

Hello to all. I’m very excited to find and interactive community to help me with my endless search for amplifier perfection. Jk.

I have a 74 super reverb. And a 1980 peavy deuce. Both run however being somewhat vintage I don’t play them super often. About a year ago I start building a “jtm 45” black flag clone. The schematic is the triode electronics build. Built a board. Populated it. Got a chassis ,drilled it, painted it, populated it. Hours of research and work I’m at the point now were I need to source transformers and tubes. However I underestimated the price of transformers which leads me to today’s inquiry.

The amp is set up with normal 12ax7 preamp, and twin el34 power tubes. Tube rectifier. Is it possible in this style of amp to use smaller transformers to not achieve the 50 watts and save some moneys by setting it up with smaller transformers to run 15 or 25 watts. I understand that it’s push pull and will still need all the tubes.

I had a baby a week ago and am trying to find any excuse to think about just about anything else.

Thank you friends . I have all the schematics and pics if needed.

[Dave]

You could set it up to run 6V6's or EL84's to get you in the 22 watt range. You could use a PT designed for a Deluxe Reverb build for that. There should be a lot of options out there for manufacturers. Same with the OT. A deluxe reverb type.


You could also get away with using the PT and the OT from a Hammond L100 series organ if you could find the amp cheap enough on EB.


If you are in Texas and close enough to where I live, gimme a holler and I can probably hook you up pretty easy and cheap. I only have probably 100 transformers that would do that job.


Dave

[Snake5150]

You could set it up to run 6V6's or EL84's to get you in the 22 watt range. You could use a PT designed for a Deluxe Reverb build for that. There should be a lot of options out there for manufacturers. Same with the OT. A deluxe reverb type.


You could also get away with using the PT and the OT from a Hammond L100 series organ if you could find the amp cheap enough on EB.


If you are in Texas and close enough to where I live, gimme a holler and I can probably hook you up pretty easy and cheap. I only have probably 100 transformers that would do that job.


Dave

Sadly I live in the land of zero freedom over on the west coast. Are those size transformers much cheaper if having to buy them outright? And using the other tubes what would change the b+ , and bias voltages?

[Dave]

And using the other tubes what would change the b+ , and bias voltages?



Yes, the B+ for a deluxe reverb type build would come in at around 420 give or take.


If you used the hammonds I was talking about, more like 400.


The bias voltage will change from one power tube to the next, but that can be adjusted for by the builder.


Personally, I wouldn't worry too much about the B+ either. You are now in the world of building an amp off spec and it will sound a "little" different anyway. The difference in the B+ will be just another "little" difference. You might love it, or you might not. Just have to wait and see.


Dave

[Snake5150]

And using the other tubes what would change the b+ , and bias voltages?



Yes, the B+ for a deluxe reverb type build would come in at around 420 give or take.


If you used the hammonds I was talking about, more like 400.


The bias voltage will change from one power tube to the next, but that can be adjusted for by the builder.


Personally, I wouldn't worry too much about the B+ either. You are now in the world of building an amp off spec and it will sound a "little" different anyway. The difference in the B+ will be just another "little" difference. You might love it, or you might not. Just have to wait and see.


Dave

Totally get that. It all started as a black flag spec clone and I quickly realized figuring out exact parts is impossible and using nos stock parts would both be difficult and costly. At this point I just want something functional that I can be proud of. I’m a tone freak but not a prude. If its loud and Marshall ish I’ll be happy. I was planning on getting Hammond transformers if the original plan goes down, any advice on other brands that aren’t as costly or should I just get over that part lol.

[Dave]

I think Hammond transformers are fine. Talking about the transformer company and not the organ company.
Weber, I think has some super cheap transformers that will get the job done if money is an object.
There are probably others too. I haven't bought any in a few years.
A lot of people like Mercury Magnetics, but you'll pay for them.
I might see what Weber has and you could probably get them cheap enough that you could swap them out later for something you like better.


Dave

[tdvt]

The AnTek toriodal transformers are way cheaper than most & have fairly good specs as far as current ratings for the $$. I have used 4 or 5 of them with good results.

Never bought one of the output transformers from them.

That said, AES & Weber have offshore products that seem to work OK, though other than the AnTeks (which I use partly due to the form factor), I try to use Hammond or Mojotone, both North American.


Also bookmarked these guys Pacific Audio Magnetics. Never used their stuff but believe they have a less-expensive off-shore line.

[mresistor]

Have you made the opening for the PT in the chassis yet?



TVDT  I'm not aware that AES has "offshore" iron. 

[Snake5150]

Have you made the opening for the PT in the chassis yet?



TVDT  I'm not aware that AES has "offshore" iron.

The chassis came with that routing done already for a lay down Marshall style. However I’m a metal and glass worker by trade and can build a plate or rack thingy to hang it or mount just about anything. I did already build a head cab so room is a small criticality.

I will check out those iron options. I would ideally like a 50 watt as planned and would like to be somewhat “close”
to spec just to ease any diagnosis of issues hood fire up. I have a variac and am planning on following rob rinettes startup guide using a light bulb current limiter. Having got hit while inside my other amp last weekend with like 390 dc, I have a new appreciation for making sure things are correct before building an expensive bomb. lol

[Snake5150]

The AnTek toriodal transformers are way cheaper than most & have fairly good specs as far as current ratings for the $$. I have used 4 or 5 of them with good results.

Never bought one of the output transformers from them.

Also



That said, AES & Weber have offshore products that seem to work OK, though other than the AnTeks (which I use partly due to the form factor), I try to use Hammond or Mojotone, both North American.


Also bookmarked these guys Pacific Audio Magnetics. Never used their stuff but believe they have a less-expensive off-shore line.

Tdvt-
If I were to get an antek one, which would I need and how do you go about mounting them? Also the pacific audio ones are CHEAP. Good eye.

[mresistor]

Where are you seeing Pacific transformers for JTM45 ?.,.   have a link?  Also  if you ever want to resell this amp, say to get a lower power amp, you will be better off getting good parts for it now.. You will get to play it in the meantime and enjoy a good clone, and could sell it easily when it comes time to part with it.
The Mojotone transformers are Heyboer and they have a very good reputation.


You could always use a attenuator on the output.  Since you mention a head can I assume you have a speaker cab already.   


If on the other hand you're not concerned about it..  then the torroidal are way cheaper, it shouldn't be hard for you to figure out how to mount a round object in a square opening.. 

[Snake5150]

Where are you seeing Pacific transformers for JTM45 ?.,.   have a link?  Also  if you ever want to resell this amp, say to get a lower power amp, you will be better off getting good parts for it now.. You will get to play it in the meantime and enjoy a good clone, and could sell it easily when it comes time to part with it.
The Mojotone transformers are Heyboer and they have a very good reputation.


You could always use a attenuator on the output.  Since you mention a head can I assume you have a speaker cab already.   


If on the other hand you're not concerned about it..  then the torroidal are way cheaper, it shouldn't be hard for you to figure out how to mount a round object in a square opening..

I’m not super concerned and if they are that much cheaper I’ll prolly go that route. I was just curious do I just try  and match the specs as close as possible for the toroidal transformers? Anything special to watch out for.


Pacific Audio transformers
Sent to me above in post
https://pacificaudiomagnetics.com/collections/all?pf_m_%3A%3Acustom_fields%3A%3Aseries=Red+Series&pf_v_amp_brand=Marshall&pf_t_amp_model=JTM45

[tdvt]

Tdvt-
If I were to get an antek one, which would I need and how do you go about mounting them? Also the pacific audio ones are CHEAP. Good eye.

They use a single bolt through the middle, usually included with the transformer along with some rubber padding & a formed steel cap. Since your chassis has a cut-out already you would need to fab a blanking plate.
I had mentioned in another thread recently for the OP to Google toroidal transformer mounting as there are some things to be aware of as far as NOT creating an external "winding" with a bracket or center bolt which can short it out.

Not sure which one you would need as I am not familiar with the amp you are building, but make note as to whether what you are looking at has 5V taps for a tube rectifier, unless you are flexible with the type of rectification.

TVDT  I'm not aware that AES has "offshore" iron. 

I was thinking of some of the $20 Champ OTs & also reverb transformers that I have bought from them & seem to remember them being imported. But they don't say either way & I would be happy to know they were made here.

[Snake5150]

Tdvt-
If I were to get an antek one, which would I need and how do you go about mounting them? Also the pacific audio ones are CHEAP. Good eye.

They use a single bolt through the middle, usually included with the transformer along with some rubber padding & a formed steel cap. Since your chassis has a cut-out already you would need to fab a blanking plate.
I had mentioned in another thread recently for the OP to Google toroidal transformer mounting as there are some things to be aware of as far as NOT creating an external "winding" with a bracket or center bolt which can short it out.

Not sure which one you would need as I am not familiar with the amp you are building, but make note as to whether what you are looking at has 5V taps for a tube rectifier, unless you are flexible with the type of rectification.

TVDT  I'm not aware that AES has "offshore" iron. 

I was thinking of some of the $20 Champ OTs & also reverb transformers that I have bought from them & seem to remember them being imported. But they don't say either way & I would be happy to know they were made here.

The specd transformer is 345-0-345
690 ct at 150ma

I found an antek one very close , if the voltage is higher than the specs transformer by 5v a side is that ok? I’m not super familiar with transformer stuff. I know larger the trans the more “headroom” but how large is too large regarding a power trans?

[Dave]

350-0-350 will give you about 7 extra volts B+ when you're all said and done. Nothing to be the least bit concerned about.


Dave