Speaking of amps that run tubes very hard....

[Randall]

I have a 1974 Alamo Montclair Reverb 2562, cathode biased with no schematic. I did a re-cap and chased out a demon or two. When I measured the two Raytheon 6V6s (one metal, one glass) I was surprised to see them running at 18.5 and 16.5 watts. The 195 ohm cathode resistor is sound, but I don't know if it is the original or intended value.

I'm at first tempted to "fix it", but I don't have a suitable resistor to play around with, and that was not the customer complaint. The amp sounds really good, so I guess I am going to go with the idea that this is how it has always been, and those American tubes can take it. I did sub a new set of JJs for long enough to measure them, and they drew even a tad more.

It bothers me, though.

[Jazz P Bass]

Here is what I have for the Montclair.

Schematic calls for a 330 / 5 watt cathode resistor.

alamo-montclair-amplifier-schematic.pdf

I am not a big fan of the metal can 6V6 tubes.

[Justin Thomas]

I'm not a fan of ANY tubes I can't see the guts of...

Justin

[mozz]

I'm not a fan of ANY tubes I can't see the guts of...

Justin

Ah, you can't discriminate based on looks, what about locktals, 7 pins, acorns, nuvistors, compactrons? Seriously, those metal 6v6's have the same spec as the glass. The metal 6l6's have the original spec of 19W dissipation. They all do get very hot though

[Justin Thomas]

It's not about the specs. It's about the fact that I can't SEE what's going on inside the tube: redplating, blue glow vs. purple glow, arcing, melting screens, lost vacuum, etc.

Justin

[Randall]

That schematic is not even close to what I have here. To start with this is a hybrid amp, only tube PI and outputs. Also it has cathode bypass cap, as well as another wire connecting the cathode to something in the preamp that I can't tell what it is.

[Justin Thomas]

as well as another wire connecting the cathode to something in the preamp that I can't tell what it is.

Some sort of negative feedback loop?
Or some sort of bias network for something?

Justin

[Jazz P Bass]

http://music-electronics-forum.com/a...9&d=1526423358

[Randall]

OK, that looks like the right one. Sure is difficult to read, tho. I THINK that is a 195 ohm cathode resistor, in which case the amp is as it was intended.

Another thing to note here is the .02 coupling caps from the PI to the 6V6s are big ceramic disks! I guess they didn't buy the orange drop/Mallory/mustard cap thinking.

[g1]

Another thing to note here is the .02 coupling caps from the PI to the 6V6s are big ceramic disks! I guess they didn't buy the orange drop/Mallory/mustard cap thinking.

Are they doing their job and keeping DC off the 6V6 grids?

[Randall]

Very good point. Indeed they are.

[g1]

Then it is probably as designed, if that 195 ohm cathode resistor is the stock value. It's impossible to tell from the 2562 schematic.
The other Montclair (all tube) schematic shows a 330 ohm there and the voltages given work out to around 12W per 6V6.