What can I use my PT for?

[Sea Chief]

Chaps- hi again. Occasional poster here (Crate Voodoo or Doggie doodo? thread etc).

I have a decent PT in a diy 'Champ' of sorts (tone & MV too/ actaully I cant remember what I made! maybe a 5F2-A of sorts but diode rectified) but think its not in right amp at all. Thing is its rated at 25w and 'only' 254v-0-254v, or 508v and 60ma.

Id'ing the unit its UK-made by transformer-electronics.co.uk, & used by Vyse amps/ can be bought from here: its the VYLM 002A sixth down here (click on white thumbnail '25' just below in middle of page for specs).. Transformers

It makes a nice clean sound in this 'Champ' ok but crank it and it barely breaks up, so Im wondering if its overpowered/ in entirely the wrong circuit in my 'Champ': Barry at Vyse from the brief info gleaned said its used "for 2x el84 or 2x6v6 type amps but the 002G is better suited to 6v6 with its 620v rating". Now a mate can kindly donate me a Champion 600 PT so logic says that's best in the ss rectified 'Champ' and then use this PT for..? well that's the Q. My hunch is its overpowered for this 'Champ' and as its a fine PT, maybe think about another amp/ circuit to optimally use it for?

Any thoughts much appreciated- Chief.

[Alan0354]

Chaps- hi again. Occasional poster here (Crate Voodoo or Doggie doodo? thread etc).

I have a decent PT in a diy 'Champ' of sorts (tone & MV too/ actaully I cant remember what I made! maybe a 5F2-A of sorts but diode rectified) but think its not in right amp at all. Thing is its rated at 25w and 'only' 254v-0-254v, or 508v and 60ma.

Id'ing the unit its UK-made by transformer-electronics.co.uk, & used by Vyse amps/ can be bought from here: its the VYLM 002A sixth down here (click on white thumbnail '25' just below in middle of page for specs).. Transformers

It makes a nice clean sound in this 'Champ' ok but crank it and it barely breaks up, so Im wondering if its overpowered/ in entirely the wrong circuit in my 'Champ': Barry at Vyse from the brief info gleaned said its used "for 2x el84 or 2x6v6 type amps but the 002G is better suited to 6v6 with its 620v rating". Now a mate can kindly donate me a Champion 600 PT so logic says that's best in the ss rectified 'Champ' and then use this PT for..? well that's the Q. My hunch is its overpowered for this 'Champ' and as its a fine PT, maybe think about another amp/ circuit to optimally use it for?

Any thoughts much appreciated- Chief.

If you have 254v-0-254v, this is for center tape and you get 254X1.414=360V unloaded. You likely get about 340VDC after loading with tubes. 340VX0.06A=20.4W. I don't think it meant to run an amp that has 25W output power. It seems like it meant 25W TOTAL power.......including filament, preamp tubes etc.

I just bought a PT for Deluxe 20W 6V6 tubes. All the ones I searched rated 120mA to 150mA. You 60mA rating is barely half. The only way you can use 6V6 is for Class A and set the bias current to less than 60mA total. Then the tubes will never draw over 60mA no matter how big a signal you pump through. You cannot use 6V6 for class AB because even if you set idle current to 50mA, it WILL draw a lot more when you hit the guitar hard. That will over stress the PT that is spec for 60mA. I don't think you can get 20W output power from this PT. My guess is 12W or even lower.

PT are not expensive, brand does not mean anything, get a new one. I paid about $50 for my PT.

[Sea Chief]

Hi Alan,

actually 12w would be a perfect size- i find the 5w Champ a bit pokey/ plasticy sounding and toy like w'out much sustain or ny breakup which is a shame, & a 22w would be too much.

Ok so can anyone point me twds a 12w circuit that this PT would suit? its surely worth using.. they're £80+on the Vyse site, and surely decent if used by a well-heeled techy like Barry Vyse seems to be.

And would the Champion 600 PT be a better bet in my 'Champ' anyway? afaik that PT has no tube rectifier ability/ wires, which Ive read isnt a big deal with such a diddy circuit, and mine isn't using the '25w' PT's ability in that dept anyway being diode rectified as I said.

Thanks RoryC

[Alan0354]

Guys, please check my work. I am calculating the primary impedance so I don't draw over 60mA at MAX input signal and fit with +B=340V. This is the graph of Tung-SoL at Screen grid=250V. But it's going give some reasonable numbers.





I calculated two points:

A) Idle at 25mA per tube.

You see I started at 25mA and draw a line to 0 grid curve intersect at 60mA. RL= (340-30)/(0.06-0.025)=8.8K
Primary = 4X8.8K=35K



B) Idle at 15mA per tube:

RL=(340-30)(0.06-0.015)=6.88K.
Primary =27.5K


As you can see, in order to use this PT, the OT has to have high primary impedance to stay within the current limit. I checked Classic Tone, I did not see anything over 8K primary. Even playing the trick of bumping up the primary by connecting 8 ohm speaker to 4 ohm tap, you only get 16K. You have to find an OT that has 2 ohm tap that limits to Super reverb. But still that is a 4K primary!!!

Looks like if somehow lowering the +B to +250VDC, then RL=(250-30)/(0.06-0.015)=4.9K. Primary = 4X4.9=19K. Now you can use a multi tap 8K primary and use 4 ohm tap to drive an 8 ohm speaker. Now you get the primary to 16K. Now you are talking.

Can anyone verify my work and my conclusion as I am still new in this tube power amp thing.

[Sea Chief]

Hi Alan0354- thanks for the help/ reply. Though Im not up to speed to comprehend too much I'll be looking fwd to reading any replies.. Im trying t go thru the basics though!

Most grateful- Chief

[Alan0354]

What you have is similar to this Classic tone PT for Champ and Princeton.

Fender Style Transformers By ClassicTone

http://www.classictone.net/40-18019.pdf


Here is the website for Fender schematic. Look at the Princeton schematic and build accordingly.

Fender Amp Heaven Schematics - Tweed Blackface Brownface Silverface Bassman Champ Deluxe Princeton Super Vibroverb Reissue

[Sea Chief]

Hi Alan- the CT looks similarly rated at 70ma.. but surely the main secondary HV pair at 650v far exceed the rating on my PT at 508v?

This 'low' 508v rating is what Im trying to establish if, it and the 'low' ma current rating, sets the basic parameter of the circuit to which its used in).

[Mick Bailey]

Did you check the output tube dissipation? I would expect that you'd get a decent breakup at full-volume if the tube was correctly biased.

There's a discrepancy between the diagram in the link and the table - diagram shows 60mA, table shows 80mA. May be worthwhile checking with the company to see which is correct.