Can someone explain transformer ma and amp ratings

[rdjones]

I recall some 100W Marshall amps have a hot combination of plate voltage and load impedance. The only thing that keeps them from red-plating is the PT voltage sag...

Happy accident, don't you think? You wouldn't design that way. Ken went the other way: overrated everything in the PT.

Except the voltage.
Ken used HT secondary voltages that ranged slightly to moderately below those of the typical Fender or Marshall.
This also contributed to the conservative design.

rd

[Reeltarded]

On the '54/'55/'56 year Fenders there wouldn't be any tone in there if the whole thing wasn't about to melt. Numb! I bet the knobs are even under by 30%. heh.

[rdjones]

On the '54/'55/'56 year Fenders there wouldn't be any tone in there if the whole thing wasn't about to melt. Numb! I bet the knobs are even under by 30%. heh.

Yeah, just think of the challenge that Leo was under to increase the durability and maintain good tone.
No wonder there was the quick evolution between the late '50s and the early '60s.

rd

[10thTx]

This is the tube data cheat sheet that I use.

with respect, 10thtx

[Structo]

Nice!

Thanks!

[yalesmith]

funny i just looked up the specs for a jcm 800 transformer and it seems way under powered using what i learned here. I would not consider a JCM 800 "vintage" either so i am not sure why it is so undervalued. I dont think that the afd 35 was built on a jcm 800 platform but rater a superlead. I think i found a good replacement if not totally overrated.

http://www.hammondmfg.com/pdf/EDB290TX.pdf

Thanks

[Firestorm]

I recall some 100W Marshall amps have a hot combination of plate voltage and load impedance. The only thing that keeps them from red-plating is the PT voltage sag...

Happy accident, don't you think? You wouldn't design that way. Ken went the other way: overrated everything in the PT.

Except the voltage.
Ken used HT secondary voltages that ranged slightly to moderately below those of the typical Fender or Marshall.
This also contributed to the conservative design.

rd

True, dat. (Trying to sound younger than I am). Good point.

[Firestorm]

On the '54/'55/'56 year Fenders there wouldn't be any tone in there if the whole thing wasn't about to melt. Numb! I bet the knobs are even under by 30%. heh.

Yeah, just think of the challenge that Leo was under to increase the durability and maintain good tone.
No wonder there was the quick evolution between the late '50s and the early '60s.

rd

I think in the 50's, Leo was chasing max output from "open source" circuits. 60's, they discovered that could push a 6V6 way past the published limits. And the 6L6GB came out. Fascinating company history; mostly unpublished, but you can suss it out some looking at the circuit evolution.

[martin manning]

funny i just looked up the specs for a jcm 800 transformer and it seems way under powered using what i learned here. I would not consider a JCM 800 "vintage" either so i am not sure why it is so undervalued. I dont think that the afd 35 was built on a jcm 800 platform but rater a superlead. I think i found a good replacement if not totally overrated.

http://www.hammondmfg.com/pdf/EDB290TX.pdf

Thanks

In the Ceriatone AFD35 layout the spec is for a "Plexi 50" power transformer, which at 312 VAC and 150mA seems too small for a pair of 6550's, but nothing says you can't do it. Maybe this is part of the recipe for this amp?

This completed AFD35 amp has a Mag Components 40-18054 50W Plexi PT: https://tubeamparchive.com/viewtopic.ph ... highlight=

After comparisons to a number of real examples using the max dissipation method I proposed above, I find using a 0.75 reduction factor seems to correlate very well for cases where the PT current rating is on the low side, pretty much nailing the "underrated" 50W and 100W Marshall cases at 150 mA for a pair of EL34's and three 12AX7's, and 370 mA for a quad. Using 100% of the Pa Max seems to work well for the opposite extreme, like the Twin Reverb example above, and Vox AC30.

Using that for the 2x 6550 and 4x 12AX7 case you have, I would get a range of 240 to 320mA (at 325VAC like the AFD35 layout shows), which still says your 290CX at 325 VAC and 207mA is too small (too small to drive the power tubes to their limits). If a 150mA 50W Plexi PT works, then you should be fine with the 290CX. As long as the load is appropriate, there won't be excessive current draw.

What issues are you having with this now?

[yalesmith]

several things:

1.) it squeals a bit, i have changed some values here and there so it does not much any more but when i max the gain knobs i still here it.... see here http://www.youtube.com/watch?v=0HMmGK1O ... e=youtu.be

2.) Really really noisy, I understand that this may be part of the design but even palm muting it still screams

3.) Sounds like crap, no grind at all super super compressed even squashed i could say. Sounds almost like a dual rectifier almost (just not as good I have one )

[martin manning]

I'm guessing your problems are due to lead dress issues, as you've obviously got some feedback where you don't want it. Compare your wiring to the amp in the linked thread, which seems to be working and stable. You could post some high-resolution photos of yours for the folks here to look at, maybe something will jump out. Do you have a schematic? It's much easier to see what the circuit looks like viz. a pictorial layout. Try to isolate the problem to one channel and/or by removing tubes one at a time.

[Reeltarded]

Out of the box. No bottom plate at all? Uhh.. GONNA DO DAT..

Has .1uF over 10k second stage? All grounds need to be pretty in that area. If you get wild squealing with gains down and master up it is in the last two stages dress.