I don't even know if I should bring this up....seems like the topic in general pisses someone somewhere off.
If it offends or is illegal, please feel free to delete it.
I recently bought & LOVE a certain 50w clone....let's says the brand is like a meteor & the model is like a super fast plane that flies from Paris to New York
Well, it's too much for me to handle.
What I'm wonderring is, is there a 6V6 model that would give the same vibe only at a lesser volume? Cathode biased class A ???
The Weber MASS does o.k., but it seems like one of those amps that needs to get up & stretch it's legs, ya' know?
The standard voltage on the output plates in that "astro-nomical" amp is supposed to be around 460V, which is quite high for a 6V6. The JJs can probably take it, but you're really pushing it, even for those.
Wife: How many amps do you need?
Me: Just one more...
I would still say go ahead, get some JJs (and keep spares on hand) and do it. If it makes the amp what you want it to be, then so what if it eats tubes.
Worst comes to worse, it can be modded with 25V zeners in series with the recto to bring he voltage down into a safe range.
Works fine but will also mess with the bias voltage in fixed-bias amps. So, slightly simpler to go in series with the recto if the amp is fixed bias. Else, you may need to tweak the bias circuit to get the voltage back up.
I use 6v6's in my Express clone to get breakup at a lower volume level for playing in the basement at home. They swapped right in place of EL-34's and didn't even need to adjust the bias. Dynamics and feel of the amp are essentially the same, a little less harsh on the attack though.
Robert wrote:I use 6v6's in my Express clone to get breakup at a lower volume level for playing in the basement at home. They swapped right in place of EL-34's and didn't even need to adjust the bias. Dynamics and feel of the amp are essentially the same, a little less harsh on the attack though.
Robert
Different animal entirely. Plate voltage in the Express is even a little low by normal EL-34 standards.
The Last of the World's Great Human Beings
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
What wattage of zener is a good rule of thumb for any amp up to say a Twin Reverb for use in series between the recto? Any issues to be concerned with?
What wattage of zener is a good rule of thumb for any amp up to say a Twin Reverb for use in series between the recto? Any issues to be concerned with?
Lemme jump in here. Let's say you've got 360 between the recto and the first filter. You want 295. That's 65 volts. P=IXE. So let's say your DC load is 200ma just for grins. The power dissipated will be 65 X .2 or 13 watts. Use some sort of safety factor here of course; 1.5? 2?. All of that of course ignores that the filter will raise the raw rectified voltage by about 1.35-1.4.
You can buy the expensive stud mount devices or just put the axial lead 5 watt jobs is series for the total amount of drop/dissipation you need. The advantage I see to putting the zeners here instead of at the center tap is that you're wacking off just half the wave at the center tap with a single zener. I think you need two, one forward and one reverse biased at the CT. I don't know if O'Connor discusses that. It may not matter. I've not played with that, though I've got a bunch of old iron and intend to right quick. On the other hand I've never used zeners as high current series devices either.
Another great way to go is to use a darlington transistor or circuit with a zener string for a reference voltage and get true regulation out of it. I wrote an article for a ham radio magazine on this approach about a million years ago. I've forgotten most of what I know about it. If you do it that way just remember to put a reverse diode to ground at the output of the darlington as transistors won't tolerate + voltage at the emitter and the downstream filter caps will destroy it.
A timely discussion.
Dan H
The Last of the World's Great Human Beings
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
In fact Jim Kelly used 6V6s in his amps at a plate voltage of 490V. He used 1k screen resistors. I have no personal experience with Jim Kelly amps since they are very rare in Germany so I cannot quote on the long term reliability.
