Don't yell at me But.......
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- digbystar
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Don't yell at me But.......
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
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
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- zaphod_phil
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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.
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Nature abhors a clean tube amp
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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.
I think converting the amp is a great idea.
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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.
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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.
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.
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- digbystar
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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 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
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- digbystar
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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.
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- digbystar
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