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Old 31st October 2012, 09:57 PM   #51
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Nice thread.

I should look at a Matchless circuit sometime, and try one out. Matchless seems to have revived the EL84 craze. I first saw one when Bob Dylan was playing thru one.
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Old 31st October 2012, 10:26 PM   #52
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Quote:
Originally Posted by cyclecamper View Post
Nice thread.

I should look at a Matchless circuit sometime, and try one out. Matchless seems to have revived the EL84 craze. I first saw one when Bob Dylan was playing thru one.
I would advise getting rid of the classic 50 and buying a ceriatone kit head.

I've repaired / modded dozens of Classic 30's / 50's and they are basically a
fantastic value amp that is built to a price point. Every where you look there
are compromises.

- Tiny transformers / OP tubes need a fan / 3 way folded PCB is not
conducive to modding and a PITA to work on / components are cheap.
etc etc etc

With the ceriatone you will have the P2P board right there in front of you to
mod and play with to your hearts content. Lot's of space, no heat problems,
ultimately better sound.

cheers

T
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Old 1st November 2012, 01:13 AM   #53
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Agreed! I've been out of touch with what's going on with amp kits. Now they have nice faceplates and everything.

Wow, I've never been to the Ceriatone site before. This is going to take me a while to absorb. Thanks.
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Old 1st November 2012, 01:34 AM   #54
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Ceriatone certainly does use large transformers.
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Old 2nd November 2012, 01:07 AM   #55
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I still want to know why one pair of EL84's has the screens connected directly to the screen + supply but the there are 100 ohm resistors between those and the screens on the other two EL84's. Why wouldn't you want the screens the same on both push/pull sets? At first I thought it was a mistake in the drawing, so I looked, and you can't miss those big 5-watters. So why would you supply 2 screens directly but feed the others with a 100 ohm resistor in series? Of course, 100 ohms is not much with tube voltages...

Last edited by cyclecamper; 2nd November 2012 at 01:10 AM.
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Old 2nd November 2012, 12:59 PM   #56
shanx is offline shanx  Canada
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I was looking at the schem for the Classic 50, and I think they have some jumpered-in resistor options if you look at the power supply feeding the plate and screen supply. The Classic 20, and 30 show similar setups. I am wondering if on a quad set of EL84s there is a reconfiguration done and those 100 ohm are to limit dissipation on the additional EL84 pair, because on the classic 20 the screen supply looks like it is developed simply in the power supply section without additional screen limiters.
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Old 2nd November 2012, 06:23 PM   #57
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I really don't know why they would feed one push/pull pair of screens differently than the other pair. The Classic 100 is almost identical to the classic 50 except there are 4 pairs of EL84's instead of 2, and they didn't do anything like this on the Classic 100.
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Old 2nd November 2012, 06:37 PM   #58
shanx is offline shanx  Canada
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Yeah it is a bit weird, the Classic 20 does not even have those separate screen resistors, it is only the voltage divider network on the power supply that is dropping the screen supply volts. That is why I suspected the added 100 ohms on second pair, keeping the total watts to a specified level.
Certainly not very straightforward
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Old 12th November 2012, 04:54 AM   #59
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OK now we're getting somewhere. I'm running a big 60-watt Edcor output transformer and the power transformer from a Peavey Classic 100 in my Peavey Classic 50. So maybe I don't need no stinking "power limiting"...

Still working on it. I have two seperate B+ supply regulators coming, one for the output power section and another for the preamp power. I
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Old 12th November 2012, 05:50 AM   #60
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I also have some chokes and electrolytics. Still waiting for the arrival of a better used VTVM I picked up on eBay before I can do much, as there are a lot of things I want to measure before I start remaking the power supply. Sold all my bench equipment a few years back when "between contracts"...unemployed. I also have this 4-gang stacked variable pot and I might use it to simultaneously vary the anode resistors in the preamp. The full-size reverb arrived; I had to order it from Korea to get the correct impedances. I would have been better to use two tanks with different impedances in parallel, one fast decay and one long maybe, as the shipping killed me. Since i have the original small tank and the new full-size tank, I might put in both with a switch. I don't know whether it will do anything at all, but I glued a small heat-sink onto the op-amp that drives the reverb. And I installed a high-low switch for the new fan.
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