Crate Palomino V50 212

[erjent]

This is quite a bit differant from the V50 112.

[Enzo]

Yes it is, glad you found it.

And thanks for posting it.

[erjent]

My next dilema is this. I need to find Bias information on this amp. LOUD tech support doesn't have any information about the Viettnamise versions of this amp. I was watching a youtube video that appears to be the same as mine, and there is a sticker that says "SET BIAS -31V FOR 100MA PLATE 1". But the fellow who made the video refrenced 6EA7 tubes. I have EL34-B tubes. Any advise would be helpful.Thanks.
erjent

[Jazz P Bass]

I think the 6EA7 should read 6CA7.
One & the same tube. EL34 ^ 6CA7.

[erjent]

Thanks Jazz P Bass!

[Jazz P Bass]

Anyway.
About the bias setting.
There are not very many dc voltages labelled on the schematic.
+ & - 12Vdc is about it.
The B+ has a 450V cap on it.
The B- has a 63V cap.
Those are the hints.
You will have to come up with a few measured voltages.
Then you can calculate what the amp "should" be set at.
Or.
You could monitor the line current to the amp & set the bias that way.
I would set it for 130 watts, idle current draw & be done with it

[erjent]

Well..., I hope I did this correctly. I put my + lead on the junction of AP2, R80, and the negative side of C47 and my - lead to chassis. With the amp in stand by I set it to -31 VDC. It goes to approx -30VDC and a bit lower in play mode. Now here is the wierd part. On channel 1 (clean) I had the tones all set to 0. The volume came up slightly through 8 then dropped out totally. When I put any Treble, Mid, or Bass in it seemed to play all the way to 10. Much Louder as Bass is added. I replaced all the pre-amp 12AX7WA's with new Tung-Sol's. Also I needed to replace my Reverb Tank. My old model was the stock 2BB2C1A. What LOUD sent me was 2EB2C1B. I now have a very high screaching when Reverb for channel 1 is on, but I get it on both channels.Does it seem feasible that the input impedience mismatch(B=150 ohm, E= 600ohm) would do this?
Thanks,
erjent

[barfoden]

Well..., I hope I did this correctly. I put my + lead on the junction of AP2, R80, and the negative side of C47 and my - lead to chassis. With the amp in stand by I set it to -31 VDC. It goes to approx -30VDC and a bit lower in play mode. Now here is the wierd part. On channel 1 (clean) I had the tones all set to 0. The volume came up slightly through 8 then dropped out totally. When I put any Treble, Mid, or Bass in it seemed to play all the way to 10. Much Louder as Bass is added. I replaced all the pre-amp 12AX7WA's with new Tung-Sol's. Also I needed to replace my Reverb Tank. My old model was the stock 2BB2C1A. What LOUD sent me was 2EB2C1B. I now have a very high screaching when Reverb for channel 1 is on, but I get it on both channels.Does it seem feasible that the input impedience mismatch(B=150 ohm, E= 600ohm) would do this?
Thanks,
erjent

Old thread, but I am surprised that he did not get a good answer..

The -31V bias voltage is static (idle) condition and should give you a total of 100mA plate current or 50mA of static plate current pr tube. But Some tubes needs less than -31V and some tubes need more negative grid voltage to bias correctly. Always measure your static plate current draw and plate voltage to get the plate dissipation in watts. You want to aim between 50 to 70% static dissipation to 12.5W to 17.5W plate dissipation in a class AB grid biased amp.

The 50mA plate current suggested on the PCB would indicate a plate voltage around 350V. Is this the voltage you get from the plate pin on the EL34 tube.

Right now I have an amp with two EL34B-STR tubes that run at ~ 412V plate at 39.8mA plate (OT voltage drop/OT resistance) when I run the amp as cold as I can get (-36.4V bias voltage). That is roughly 66% of max dissipation. In my particular 1x12 combo amp that sounds a bit too hot. A little more noise and less punchy in the bass than I wanted.

[Rock-It]

This is an old thread, so if mistakes were made it's history. I have a cream tolex Crate Palomino V50 made in Vietnam. I was also a service tech in a pro audio service center authorized on Loud Technologies products (and this is one of them). To bias this properly, you need to be able to measure the plate voltage on the EL34's when B+ is applied (Standby Off). Also, you need a way to measure the plate current. That may require something like a Weber Bias-Rite meter. or something cheaper like is found here: https://www.eurotubes.com/store/pc/bias%20probes.htm. You will need to completely remove the chassis from the cabinet, and safely set it up so the bias pot on the main PC board is accessible AND the power tubes have enough room to extend after plugging them into the bias probe socket (which also is plugged into the tube sockets). This, of course, implies that you first disconnect the speaker wires, reverb tank wires, and make sure the AC power cable is free. Then unscrew the chassis screws (4 on the sides & 2 on top) while holding the loose chassis for removal. This is delicate because you don't want to rip the tolex. You have to work the chassis out carefully and be ready to set it down on a table top. Then you plug in your bias probes, connect your speakers, turn your volume controls down, turn power on safely. Measure plate voltage first. Then measure plate current. Then set the bias in Milliamps. Here's how you calculate: 25 divided by the Plate Voltage, X .7 = Bias Plate Current. For instance, if you measure 408VDC, then it's 25 divided by 408 = .061. Then, .061 X .7 = .0427. So set the Plate Current to .042 Amps (or 42 Milliamps). The formula for setting bias is 25 Watts Dissipation (that's for an EL34 tube), divided by the plate current to give you 100% Dissipation. That would be the setting if you want to run the tube wide open HOT!!! (not wise). You can safely run it anywhere from 65% to 85%. The HIGHER the dissipation, the hotter and better the tone, but less tube life. The LOWER the dissipation, the colder and starker the tone, but longer tube life. I like to set it at about 70% to get the best of both worlds. The tube just comes out of crossover distortion at 65%, so I definitely want it higher. This is a LONG explanation, but I just won't do it any other way. You can also use the 1-ohm resistor method to measure in Millivolts, but that's an entirely different episode boys and girls. Have fun.

[Rock-It]

This is an old thread, so if mistakes were made it's history. I have a cream tolex Crate Palomino V50 made in Vietnam. I was also a service tech in a pro audio service center authorized on Loud Technologies products (and this is one of them). To bias this properly, you need to be able to measure the plate voltage on the EL34's when B+ is applied (Standby Off). Also, you need a way to measure the plate current. That may require something like a Weber Bias-Rite meter. or something cheaper like is found here: https://www.eurotubes.com/store/pc/bias%20probes.htm. You will need to completely remove the chassis from the cabinet, and safely set it up so the bias pot on the main PC board is accessible AND the power tubes have enough room to extend after plugging them into the bias probe socket (which also is plugged into the tube sockets). This, of course, implies that you first disconnect the speaker wires, reverb tank wires, and make sure the AC power cable is free. Then unscrew the chassis screws (4 on the sides & 2 on top) while holding the loose chassis for removal. This is delicate because you don't want to rip the tolex. You have to work the chassis out carefully and be ready to set it down on a table top. Then you plug in your bias probes, connect your speakers, turn your volume controls down, turn power on safely. Measure plate voltage first. Then measure plate current. Then set the bias in Milliamps. Here's how you calculate: 25 divided by the Plate Voltage, X .7 = Bias Plate Current. For instance, if you measure 408VDC, then it's 25 divided by 408 = .061. Then, .061 X .7 = .0427. So set the Plate Current to .042 Amps (or 42 Milliamps). The formula for setting bias is 25 Watts Dissipation (that's for an EL34 tube), divided by the plate current to give you 100% Dissipation. That would be the setting if you want to run the tube wide open HOT!!! (not wise). You can safely run it anywhere from 65% to 85%. The HIGHER the dissipation, the hotter and better the tone, but less tube life. The LOWER the dissipation, the colder and starker the tone, but longer tube life. I like to set it at about 70% to get the best of both worlds. The tube just comes out of crossover distortion at 65%, so I definitely want it higher. This is a LONG explanation, but I just won't do it any other way. You can also use the 1-ohm resistor method to measure in Millivolts, but that's an entirely different episode boys and girls. Have fun.

[Petr]

Hi,

may I ask you for the schema of this amp, please? The link above doesn't seem to work for me. I have this amp on my bench right now, changing the tubes, biasing etc. But it hums, so I suspect at least one of filtering caps is faulty. According to the owner they have been replaced in the past. So I'm curious about the original specs of those filtering caps. I can see 1x 100uF/450V and 4x 47uF/450V. Does it match original specs of this amp? Many thanks for some help!

[Petr]

I found it! Thanks to Jazz P Bass answer in this thread:
https://music-electronics-forum.com/...ad.php?t=39068

[Rock-It]

You found it!

I found it! Thanks to Jazz P Bass answer in this thread:
https://music-electronics-forum.com/...ad.php?t=39068

Yes, Jazz P posted the correct schematic. I'm surprised someone actually had it. All of the threads I have ever followed had an incorrect one. I got mine directly from Loud since I was an authorized tech. They had to do some "way-back" searching too. Let us know how your research with the caps goes. I've replaced caps before for buzz in these amps and it never seemed to matter. All my experiences wound up with tube replacement and proper biasing (a real involved procedure but worth it). It looks like I gave detailed instructions back in 2015. Hmm. Come to think of it, I haven't biased that amp very recently. Lol.

[Petr]

Well, in my case I decided to replace all those 47 uF caps as I have found one of them faulty. But indeed then I replaced all tubes and properly biased the amp.