Tweed Champs what do you like?

[Mark]

http://www.youtube.com/watch?v=1_k-KJlgJfU

The Mosaic has an Mercury Magnetics oversized output transformer.

http://www.youtube.com/watch?v=D5iWv3DPaHk

[Colossal]

http://www.youtube.com/watch?v=1_k-KJlgJfU

The Mosaic has an Mercury Magnetics oversized output transformer.

http://www.youtube.com/watch?v=D5iWv3DPaHk

Actually you're right Mark, that's a bad example. The Mosaic does have a custom OT and impedance, so it's a Champ but with a 'little more'. A fantastic sounding amp in Greg's hands.

[rp]

I'm curious about this one: http://store.triodestore.com/40-18031.html
They little one they offered for Champs for many years was stinky, this looks about right, the dual primaries are nice but my Champs with the Allens have 4/8 taps and I tried mismatching giving me 3500 / 7000 and while I could hear it, it wasn't worth troubling over, 3500 was a touch thinner. I like the higher Pz I decided.

[Mark]

the amp also broke up a lot earlier too.

I should point out that I didn't have the feedback loop hooked up to the rewound transformer as it was a hassle to find a switch that would handle the current. I'll put the transformer into the amp tonight and see how the feedback affects the gain. The Roughneck has a 68K F/B resistor, I'll put a 33K (33K in parallel with 68K is 22K) on a switch to compare the stock feedback with the Kendrick value.

[Mark]

I've had a reply from Mercury and they recommend a larger transformer if you're after more bass and mids.

I think the larger output transformer is a good idea if your building a Champ and may be using a ceramic speaker.

What I'm not taking into consideration is the effect of the alnico speaker evening out the response of the amp. I suspect the larger transformer is a good idea either way.

The update:

I have been using the amp as I received it with a 6L6 and a GZ34, I just put a 5V4 and a GE 6V6 into the amp and it sounded a lot bigger, not as big as the transformer with the 5K primary, but definitely more amp like, the amp also broke up a lot earlier too. I'm wondering why Kendrick would send an amp out with a valve compliment that would make the amp sound worse?

The rewind of the output transformer sounds good, the amp is loud enough. I dare say the mismatch of the 8K primary and the 6L6 doesn't work real good?

The next update:

I've got the rewound transformer into the amp, and it doesn't sound anywhere near as good as the larger 5K transformer.

[rp]

Mark, any idea what the PZ of the Mercury is? Supposedly they've blueprinted all the orig trannies and that's part of their shtick. I asked on here and did a lot of web searching and there is no exact info on the tweed champ OTs, whether 5K, 7K or 8K. Given the lack of info I've no idea why it's universally assumed the tweeds were 5K. The BFs were 7 or 8K IIRC. Someone needs to blueprint their original and put it on the web and settle it for all time.

[Mark]

As far s I know the primary impedance for a 6V6 is 8K. I would have thought a 5K primary would have been pretty tough on a 6V6. I was using 5K with a 6L6 and the power transformer was getting really hot.

I don't know what impedance the Mercury transformers are, and MM never give out specs, so you're not to know.

[rp]

As far s I know the primary impedance for a 6V6 is 8K. I would have thought a 5K primary would have been pretty tough on a 6V6. I was using 5K with a 6L6 and the power transformer was getting really hot. I don't know what impedance the Mercury transformers are, and MM never give out specs, so you're not to know.

In my web searching I found most peeps use 5K for tweeds but 8K is more correct by the charts. Fender had real engineers and the did tend to stick to theory, especially in the early days. Lowering the Pz gives more power / less headroom, no? I can't see why Fender would be trying to get more power / less headroom from a '50s student amp. Anyway my fave champs have the Allen which is 7K IIRC.

[martin manning]

Allen's Champ OT's are 8k. I think with the load line and voltage these things are running higher Zpri will produce more clean power and headroom.

[Mark]

Fender had real engineers and the did tend to stick to theory

I thought a lot of the circuit were lifted out of the valve data sheets.

The data sheet says 5K at 250VDC, and 8.5K at 315VDC.

[Colossal]

Looking at the 5E1 and 5F1 schematics, there are two PT secondaries generally cited; 250-0-250 (5E1) and 330-0-330 (5E1/5F1) and two OTs, 5k and 8k. It seems they went from the 5E1 design running 250-0-250 and a choke (470R cathode resistor), to the later 5F1 running 330-0-330 (370VDC plate voltage) and 8k OT, but with a 10k choke resistor (probably to cut cost but still preserve the screens by dumping some voltage). The schematic still shows 21V at the cathode at 370VDC plate.

[Mark]

Wouldn't 250 - 0 - 250vac secondary still equate to 280VDC on the plate, in which case the primary impedance should be some where between 5K and 8K?

The point being that I don't see the Champ as an exact science but whatever was convenient.

[rp]

The point being that I don't see the Champ as an exact science but whatever was convenient.

Very true but when trying to make an exact clone it'd be nice to know what the orig had. So Mercury won't even give you specs if you ask? I couldn't care about their pricing or hype but engineering firms that don't publish easily available, complete specs are unacceptable

[martin manning]

Unfortunately the old Fender Champ schematics do not list transformer numbers. However, the Fender PN for the '57 Champ is 022905, which shows up at AES in a Fender Champ replacement part and also in a Hammond equivalent. These are both spec'd 7k primary.
http://www.tubesandmore.com/products/P-TF22905
http://www.tubesandmore.com/products/P-T1750C
The '57 Champ schematic also shows 350V B+. Replacement PT's cite 125P1B as the Fender part, and are 325-0-325. I would think that would produce closer to 400V. I don't believe a 5Y3 will drop much voltage at this relatively low current.

[Colossal]

Mercury should tell you the immediate specifications for any ToneClone part, such as its primary or secondaries, current handling, etc. A ToneClone part is an PT or OT that was reversed from an existing classic amp. The problem is that Fender, like Marshall, like Vox, created a very messy bread crumb trail in that there is a lot of overlap in parts and sometimes parts with the same OEM id could have differing specs. There are so many ToneClone pieces in Mercury catalog because there was huge variance in the Holy Trinity's part sources and many evolutions of the same product lines over the years. 7ender even states at the top of some of their schematics, +/-20% variance to nominal voltages.

RP, what part were you specifically looking for the specifications for?