What's the plate voltage of an RM50? Need Bias help

[Rod]

Wondering about where to set the bias on my RM50 using KT77's...Do they bias the same as EL34's?

 

[drewiv]

I'm guessing the KT77s will be the same as EL34s.

Not sure of the plate voltage...

 

[Rod]

Thanks Drew.. I was asking about plate voltage because I have a bias calculator and it will give me an accurate bias figure...but that chart is great,,,,thanks again

 

[drewiv]

Thanks Drew.. I was asking about plate voltage because I have a bias calculator and it will give me an accurate bias figure...but that chart is great,,,,thanks again

I'm sure someone around here knows the plate voltage. I'm not an amp tech, I just use my simple little chart from the manual and hope things go well.

 

[Mattfig]

Once I get home this afternoon I will check mine and write back.

 

[Rod]

Thanks guys....I know that 2kceeb ?...knows it He's a great amp tech from my neck of the woods..maybe he will pipe in...

 

[joey_truelove]

I'm guessing the KT77s will be the same as EL34s.

Not sure of the plate voltage...

Just don't be too sure. The KT77s are 32W each (max), so that may differ slightly. As with KT66s they really like running hot, IMHO, but your milage may obviously vary.

 

[Mattfig]

Just checked mine....Mine reads 513....Pretty hot stuff....

 

[Jaded Faith]

That 513 is really high. Most of the RM amps tend to range between 470-500 here and my wall voltage is typically around 120-124V.

 

[kc2eeb]

Thanks for the compliment! Your plate voltage will vary with your line voltage. My amp averages 505-510 VDC depending on the time of day.
Hey Matt, are you using a power conditioner?

 

[Mattfig]

Hey Matt, are you using a power conditioner?

All my amps are on a power conditioner - Except the RM50 I just checked. I had to move it around a bit and it wound up being off any conditioner. After that hot reading, I think I'll move it back....

 

[Rod]

Thanks everyone for piping in... So... according to this bias calculator... at 500 volts, the bias for an el34 should be only 28mv per tube...
Drew's Randall tube bias recommendation sheet says quite a bit higher..
What should I set the bias to? Is a KT77 going to be any different ?

 

[drewiv]

Thanks everyone for piping in... So... according to this bias calculator... at 500 volts, the bias for an el34 should be only 28mv per tube...
Drew's Randall tube bias recommendation sheet says quite a bit higher..
What should I set the bias to? Is a KT77 going to be any different ?

Where's Bruce? :lol:

 

[joey_truelove]

Thanks everyone for piping in... So... according to this bias calculator... at 500 volts, the bias for an el34 should be only 28mv per tube...
Drew's Randall tube bias recommendation sheet says quite a bit higher..
What should I set the bias to? Is a KT77 going to be any different ?

The KT77 should go right between the E34L and the 6550, really. Unless of course you want more glass-y sounds by running it cold.

Your best bet is really measuring the voltage and estimate the bias current from that. Some valves draw more than others, which lead the PT to drop in voltage. But you're correct in that the higher the plate voltage the less the bias current to equal the specified/ desired dissipation.

 

[Rod]

JOEY... that would be about 40ma per tube....