Guitar Valve Amp Output Transfomers

[shunt94]

Hey,

I was thinking about building a valve guitar amp following this Schematic:
Marshall JMP 2204

I was going to put a 100w Power transformer from an old 'Sound City' amp (Making the 50w version of the Marshall amp as I don't really have that much money for valves! But can always add in the extra part of the circuit )

Basically, Its the Choke and output transformer that is worrying me.
I have a Utc a-20 Output transformer from a previous Transistor amp build and was wondering if that will do the trick?
And does anyone know of any cheap but good Chokes that I could buy?


Many Thanks!

 

[HollowState]

I have a Utc a-20 Output transformer from a previous Transistor amp build and was wondering if that will do the trick?
And does anyone know of any cheap but good Chokes that I could buy?

Surely you have the number wrong. A UTC A-20 is a 30 milliwatt line output transformer. For the choke, try Edcor or Hammond.

 

[PeterDupont]

Mercury Magnetics -- The Guitar Amp Transformer Company

These are among the best.

Regards, Peter

 

[ChrisA]

Basically, Its the Choke and output transformer that is worrying me.
I have a Utc a-20 Output transformer from a previous Transistor amp build and was wondering if that will do the trick?

Almost certainly "No". You will need an Output transformer with an impedance ratio of roughly about 6,000:8

And does anyone know of any cheap but good Chokes that I could buy?

Buy the transformer and choke at the same time and save on shipping. stf-electronics.com has good prices on Hammond parts. Choke for maybe under $20 and a output transformer suitable for your amp for about $75

They have metal chassis too, good prices, may as well get it all at once.

 

[scott17]

I bought transformers from this site when I built my Champ 5F1 clone and I'm very happy with the quality.

They have Marshall style transformers also. Great prices.

Transformers for Tube Amps

 

[tinitus]

Hey,

I was thinking about building a valve guitar amp following this Schematic:
Marshall JMP 2204

looks complicated

 

[wakibaki]

Pick a transformer recommended for the application (50W Marshall) as it will have a critical impact on the sound you get, you can use an oversized one safely, but it will tend not to produce the distortion (typical sound) Marshall users expect.

w

Oh, this applies to the power transformer AND the output transformer.

 

[Gilgy]

I was going to put a 100w Power transformer from an old 'Sound City' amp (Making the 50w version of the Marshall amp as I don't really have that much money for valves! But can always add in the extra part of the circuit )

I'm guessing the Sound City had four EL34's and you're talking about making a 50 Watt version with two EL34?

You can't simply omit two valves and use the same transformer, the impedance ratio will be wrong.

EDIT: ignore me, I didn't read the bit that said "power transformer". You'll be fine using the power transformer, just the output transformer will have a different impedance ratio from the design value on your schematic.

 

[PeterDupont]

It's a strict rule to know a certain degree of amp-design. I have never, ever gone to more extend than switching an output-tranni in a Super-reverb to one from a Showman just to be able to use 4 Ohm instead of 2 Ohm, loading the secondary near perfect. And the heavier iron was just disappointing soundwise.
Keep values as they are - unless tweaking with eq-components.

 

[tinitus]

from the nature of your questions I conclude this is your first tube amp, since you ask about chokes

this one looks a lot easier to build
I have seen it in several places, so I'm not sure who designed it
but I guess its a proven design

 

[PeterDupont]

The Mercury Magnetics choke
Mercury Magnetics Axiom MAR100-C
costs around 30$.
It's a near perfect replica of the original choke, that was a little undersized, BUT tributed to the overall virtues of the amp (with hundreds of other parts that contributed to the "tone" that is hard to DIY.

Regards, Peter

 

[danFrank]

In my opinion, Mercury Magnetics' products are WAY too overpriced. They justify it with long winded maketing mumbo jumbo to make it seem that their transformers are unique and will make you sound like Hendrix when you play through their transformers. This might fly with Hi-Fi transformers, but quite frankliy, guitar transformers are not wound that critically. In fact to get that "classic" tone, the cheaper the output transformer is wound, usually the better.
I guess they charge so much in order to pay their marketing dept.
Daniel

Try Triode Electronics or Antique Electronic Supply for Transformers / chokes. Their prices are better.

 

[shunt94]

Hey,

Thank you all for the feedback!
I've got the power Transformer off Ebay today. So, after checking to see if the voltages are correct, Il think about investing more money into building the 100w version of this amp... I'll have to think about that though... I may just make the 50w version and if that sounds awful, build the 100w version

ChrisA: Thanks for the info!.. .I think il take your advice and buy everything at once, It seems like a plan!.. I'll buy a separate output transformer as well

tinitus: Yea, This will be my first amp. My brother built a hi-fi amp and got loads of info from this site! I was just hoping to do the same. I think I should be able to follow the diagram... but I'll need to do a lot of testing! Thanks for the extra diagram though, I may build this as a test and then just go up from there

Many Thanks to everyone else as well! - Answered all my questions!