Don't yell at me But.......

digbystar · Post by **digbystar** » Fri 04/03/09 11:19 pm

I have a Peavey classic 50 which uses 3 @ 12ax7, 4@ 6bq5's. It now has transformers from Mercury Magnetics and Weber Blue dog alnico's .I'm wondering if this is a good platform ( Trans, Chassis, Cab, Speakers, etc.) to start with? Do you guys think these trannies are plug and play with the 36 watt circuit board in the download section?

While I'm asking, What is the best way to do a 1/2 power on these? Thanx alot for the help! and I look forward to talking to you guys in the future!,

Digs

Post by **zaphod_phil** » Sat 04/04/09 7:32 am

Probably OK, but if that amp was getting 50W out of four EL84/6BQ5s, what kind of voltage is there on those tubes? I think it would be a good idea to measure that from your working amp (taking care not to kill yourself) before you take it apart. You might need to use one or two tricks to reduce that voltage down a bit. Or it may just be that those are 50 marketing watts.

Apart from that one concern, those MM transformers should sound real good in a 36W.

Post by **rjgtr** » Sat 04/04/09 8:49 am

Just to add to the conversation - if you find the voltages high, just make sure you use a high enough screen resistor to lower the voltages below 300V. From looking at the schematic they are using a 400ohm resistor between the output transformer filter node and the screen node in the power supply. This resistor is 1kohms on the 36watt so the Peavey is really punishing the EL84 screens.

I think converting the amp is a great idea.

digbystar · Post by **digbystar** » Sat 04/04/09 9:07 am

Wow, thanx for the help guys I will measure the voltage today. Pin 7? and a different resistor is enough on the volts. No zeener needed? thanx again,

Post by **zaphod_phil** » Sat 04/04/09 9:24 am

You may need to use some zeners in addition to what rjgtr said about the screen resistor. We will know when you get the voltage measurements. If the voltages are too high the amp won't sound that good. Yes, pin 7 of any of the power tubes is where to test.

katopan · Post by **katopan** » Sat 04/04/09 3:51 pm

The Carvin Vintage 50 seems to be punishing a quad of EL84s in a similar way. According to a schematic I dug up it's got 455V on the OT centre tap and 445V with 350ohm resistors on the screens. My friend who recently bought it loves the tone, but I wonder how long that's going to last with those voltages.

Post by **zaphod_phil** » Sat 04/04/09 6:22 pm

Seymour Duncan had an amp that ran a quad of EL84s at 560V for 50W out.

The secret to how it worked was that the screen grids were at 280V (560V/2). However the tone was pretty sterile, which seems to usually be the case with EL84s much above 400V.

digbystar · Post by **digbystar** » Sun 04/05/09 9:19 am

I'm getting 432 in stand by, then when I kick it on it drops to 403.

veets · Post by **veets** » Sun 04/05/09 5:30 pm

The loss of 29 volts is normal going from standby to run. Still, 403 VDC on the plates seems a tad hot to me. What do you have for voltage on G2 ?

digbystar · Post by **digbystar** » Sun 04/05/09 5:43 pm

G2? sorry i'm a newby

Defdaddy · Post by **Defdaddy** » Sun 04/05/09 6:00 pm

G2 = grid #2 = the screen on a pentode. Pin 9 on your EL84

digbystar · Post by **digbystar** » Sun 04/05/09 7:35 pm

I let the amp warm a bit this time and both pin 7 and 9 are the same at 394-396

Post by **rjgtr** » Sun 04/05/09 8:48 pm

I think if you build a 36watt (well more like 45watt), then I would definitely suggest you adjust the screen voltage. However, I don't think the 390-400V on the plates will sound bad if the screens are good. Most 18watts run between 320-350V on the plates. 20watt amps are more like 375V.

If the voltage is too high, then using zeners as phil suggested or a VVR circuit to adjust the B+ might work. Another option is to take the 1K 10w resistor before the screen tap to 10k or just taking the 8.2K in the B+ line before the phase inverter higher to 20k 5watt would help. I've found that if you can get the preamp voltages right it will go a long way to keeping the amp warm. The extra power tube voltage might just make the low end a little tighter.

digbystar · Post by **digbystar** » Mon 04/06/09 11:55 am

Great , Thank you very much for the info. I'm gonna start buying parts right away. I'm waiting for a cheap board to come up on ebay.
I belong to a couple other forums (shovelheadUSA, Tokai) and this is the liveliest one by far, I'm stoked. thanx again, Dig

Defdaddy · Post by **Defdaddy** » Mon 04/06/09 1:27 pm

Norm (EBE) makes nice boards:

http://www.18watt.com/modules.php?name= ... ic&t=20757

mcrracer · Post by **mcrracer** » Mon 04/06/09 2:03 pm

digbystar wrote:Great , Thank you very much for the info. I'm gonna start buying parts right away. I'm waiting for a cheap board to come up on ebay.
I belong to a couple other forums (shovelheadUSA, Tokai) and this is the liveliest one by far, I'm stoked. thanx again, Dig

Make your own board...can't get any cheaper than that. Use eyelets and 1/16" thick Garolite. Do some reading. It is simple enough to do and plenty of layouts and pictures. Eyelets around 2 or 3 cents a piece if you look ( contact me if you just can't find them) Board material 24" by 24" between $13. and $20. You can cut a bunch of boards out of that. Try it.

digbystar · Post by **digbystar** » Sun 04/19/09 12:42 pm

Yes making it would be cheaper, but I figured I'd be better off to see one made before I try it on my own. I did get one from Norm (nice) and now I'm getting closer with the parts. I tried searching "VVR" but didn't get much. What is it? Can I build it myself? It seams like people are talking about patents/copyrights and such.

digbystar · Post by **digbystar** » Sun 04/26/09 9:59 pm

Is it better to start another thread then to add on to this one even if it is talking about the same amp?

anyway, would changing the transformer to a typical one be better in the long run then resistors and zeeners?

any suggestions on wich one? thanx again

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Don't yell at me But.......

Don't yell at me But.......