Metropoulos Forum

Hello guys,
I've built and rebuilt amps for many years but I have a question, or I guess I am looking for opinions also. I am working on a 4 x EL84 36 watt Clone head with a circuit roughly patterned after the Weber 6M36 head. I say roughly because the builder that built this amp had really no idea what he was getting into or what he was doing. I have had to rebuild 4 of his amps, this one now the 5th, all of them disasters that I have resurrected from near death. Here is the thing, the OT he put in this amp is a nondescript unidentifiable piece of iron that, after measuring, showed to have a primary impedance at 8 ohms of 2300 ohms. A 4 x EL84 amp should have an OT impedance of roughly 4K ohms. I have looked at the Weber OT as a replacement for that head and it is a 4K primary impedance, but the cost on that OT is $58 Plus shipping. What I have been considering as a more cost effective replacement is the Hot Rod Deluxe replacement P-TF50438 which has an impedance of 4250 on the primary with 4/8 ohm secondaries and is a much better price of $31.95 and is rated at 40 watts. I am trying to keep the cost down on this due to the fact we have already had to replace the PT with a Hammond because the PT he put in the amp only had a 6.3V winding rated at 2.5 amps and just the EL84s will draw more than that on their own and this along with other PT issues was wreaking havoc with the Power tranny making it run hot as hell and making everything unstable. I am thinking, while not an EXACT match, at 4250 ohms on the primary and 40 watt rating that it would certainly do the trick.
What is you guys' opinion tech wise?

Thanks,
avguy49

the Z is fine but I'm not sure about the other specs

Of which other specs are you speaking?
avguy49

frequency response, winding patters, steel quality, etc will affect tone and response a lot

avguy49 wrote:Hello guys,
I've built and rebuilt amps for many years but I have a question, or I guess I am looking for opinions also. I am working on a 4 x EL84 36 watt Clone head with a circuit roughly patterned after the Weber 6M36 head. I say roughly because the builder that built this amp had really no idea what he was getting into or what he was doing. I have had to rebuild 4 of his amps, this one now the 5th, all of them disasters that I have resurrected from near death. Here is the thing, the OT he put in this amp is a nondescript unidentifiable piece of iron that, after measuring, showed to have a primary impedance at 8 ohms of 2300 ohms. A 4 x EL84 amp should have an OT impedance of roughly 4K ohms. I have looked at the Weber OT as a replacement for that head and it is a 4K primary impedance, but the cost on that OT is $58 Plus shipping. What I have been considering as a more cost effective replacement is the Hot Rod Deluxe replacement P-TF50438 which has an impedance of 4250 on the primary with 4/8 ohm secondaries and is a much better price of $31.95 and is rated at 40 watts. I am trying to keep the cost down on this due to the fact we have already had to replace the PT with a Hammond because the PT he put in the amp only had a 6.3V winding rated at 2.5 amps and just the EL84s will draw more than that on their own and this along with other PT issues was wreaking havoc with the Power tranny making it run hot as hell and making everything unstable. I am thinking, while not an EXACT match, at 4250 ohms on the primary and 40 watt rating that it would certainly do the trick.
What is you guys' opinion tech wise?

Thanks,
avguy49

2.3k/8ohms is the same as 4.6k/16ohms. if he has a 16 ohm cab he can use (and you feel the trannie is physically large enough by 4 el84 amp standards) you're good to go. it's condition,sonics, etc. are other matters entirely since it's a salvaged piece. rh

Well, He pretty much universally uses 8 ohm cabs. All of the regular cabs he uses are 8 ohms. The other thing about whatever this old OT is is that I just didn't like what I saw on the scope testing it. It just didn't respond or look right to me somehow. I am going with the Hot Rod Deluxe OT. I know that a lot of guys that have the Hot Rod Deluxe amp replace these in those Fender amps but I think this one will be the best bet for this situation overall. The primaries are right on and it has a 4-8 ohm tap secondary and rated at 40 watts. I just have a gut feeling this one will rock in this amp. It should be in next week and I will let you know how it plays out. IF it works as well as I think it will then I may use that one again in a 36W EL84 build. I have noticed that finding a good, solid, and ECONOMICAL OT for this config is a bit of a challenge. The next one up in line is the Weber OT @ $58 something bucks. There are a LOT of players in my area that play either 18W or 36W EL84 amps and I am working on a few prototype designs of my own, so we'll see how it plays out. Who knows, I might just be wrong, but I really don't think so.

Cheers guys,
~Avguy49 ~Philly