old thread

[utervo]

Thanks again.

I'll get all of the parts suggested and fiddle around and see what sound good.

So it's metal oxide for the PSU, carbon comps for the plates and metal film elsewhere. F+T caps for PSU, Vitamin T's (perhaps Mallory's for comparing) for coupling and F+T or Evox Rifa for the cathode bypass caps.

Perhaps I'll change the transformer to 8W Champ replacement the shop carries, it says Made in USA, maybe it's from the same source as Hoffman's as they seem 8W also?

[utervo]

I believe the transformer they sell might be the same that Weber sells, does anyone know if it's good?

[CaseyJones]

You can't go wrong with your parts as listed above. The right parts are a good start. There are lots of vintage amps that were built with parts that aren't as "good" as some of today's "junk" parts.

The Weber Champ transformer would be the WO22905M. It's clearly marked WO22905M unless your vendor removes the markings. It will not say "Made in the USA" because it isn't made in the USA. It's 8k into 4 and 8 ohms. It looks like a stock Champ transformer, it acts like a stock Champ transformer. Weber says it's rated for amps that produce between 6 and 15 watts. It's worthwhile to buy the WO22905M rather than the WO22905 because the WO22905M has an 8 ohm tap, an exact Champ replica is for 3.2-4 ohms.

Your choices here: If you're building a tweed replica use the WO22905M, if tweaking is part of the plan use the WSE15 or the WSE25 or buy a genuine Hammond 125ESE.

There is no clear choice for the "best" transformer. IMHO there are no "bad" Champ transformers. If you want a replica of a screaming tweed then use a stock replica transformer. If you want to use the 5F1 circuit and tweak to something different then try upgraded transformers.

[utervo]

I guess I'll go with the Hammond, the 125ESE is 15W?

It's getting comfortably confusing as I get closer to ordering.

[CaseyJones]

I guess I'll go with the Hammond, the 125ESE is 15W?

It's getting comfortably confusing as I get closer to ordering.

It's getting confusing because you're making it harder than it has to be.

When Fender built the originals they were only built as good as they had to be. "As good as they have to be" is by 1950s standards. I can further qualify that by saying they were as good as they had to be by '50s Fender standards, it just turns out that Leo and Doc were good at what they did.

Hammond makes a line of single ended transformers, the 125ESE is their top specification SE in the 125 series. The 125ESE is a 25 watt transformer so it will work with nearly any tube you might want to use in the future. It's more transformer than you really need.

If you want to learn build two of these. Build the first one with the least expensive junk you can find, there are only 11 resistors and 7 capacitors. I'm not joking, use junk. Use old parts left over from other projects or salvaged parts. Use the least expensive transformers and the least expensive tubes you can find.

Do the opposite on the next one. Then compare. Don't take my word for anything. I won't be insulted, there's a scientific approach and that's it.

Once you have two operable units crank them both up and decide which has "mojo" and which has "suck". Seriously, I can build an amp with excellent parts and it will still suck. I can build an excellent amp with "junk".

[utervo]

Well, after all I managed to send my order. Will take a while to come as it's our independence day tomorrow.

Meanwhile has anyone tried these caps:
http://export.farnell.com/jsp/Passive+C ... tid=206149

[utervo]

Seems I'm getting quite far from the original champ. I scored some 6AQ5 tubes and I'm planning to use them, they should fit with no problems?

For the rectifier, will GZ30 fit ok?

[mhuss]

Seems I'm getting quite far from the original champ.

Yes, now you've moved to "champ designed by committee."

--mark

[utervo]

Well I don't mind it, as long as I get it safely built and working. From there on I can start experimenting more and learn myself.

[CaseyJones]

For the rectifier, will GZ30 fit ok?

GZ30/5Y3?

The Champ is pretty light on current demand so just about anything will work in there for a rectifier. As usual there are options with benefits and drawbacks:

The 5Y3 is used in the stock circuit. They're cheap and available, you'll need to use an octal socket obviously but you can use that to your benefit. The benefit is that if you want to se your chassis as a platform for experimentation other octal rectifiers will fit, obvious alternatives would be the GZ34/5AR4, maybe a 5V4 or a 5U4G. Make sure you have 3a/5v available if there's a 5U4G in your future.

If you using a 6AQ5 you might want to consider a 6X4/EZ90. Like the 6AQ5 it fits in a 7 pin miniature socket. The asset of the 6X4 is that it fits in a compact socket and it doesn't need a 5 volt filament, the drawback is that you can't swap it like the octal types... and it's limited in its capacity.

A 6CA4/EZ81 is cool. It fits in a 9 pin miniature socket, it doesn't need a 5 volt filament and it "thinks" it's a little 5AR4. It's a perfect rectifier for slightly larger and more complicated amps like the various 18 watters.

You can omit the tube rectifier entirely and just use a couple silicon diodes.

If you're using a 6AQ5 tube rather than a 6V6 make sure your plate voltage is down at original tweed Champ specs. "By the book" ratings place the maximum plate voltage and the maximum screen voltage at 250 volts each.

[utervo]

Good morning.

I have the stuff here now, well most of it. Do you have any additional layout tips, which way and were to mount transformers, boards...? I have a pretty big box, Hammond 1444-28.

I am also wondering how the mods CJ suggested will affect in a technical sense.

I think I should probably also get an impedance selector for the Hammond, though as I just woke up I have a little hard time following how their system works with so many possibilites on the transformers...

For the b7g base I just change the wiring as to match the octal?

[davent]

Good morning.

...
I think I should probably also get an impedance selector for the Hammond, though as I just woke up I have a little hard time following how their system works with so many possibilites on the transformers...

Hello,

Page 2 of this pdf has a couple impedance selector switch hookup diagrams for the 125ese.

http://annex.ax84.com/media/ax84_m325.pdf

dave

[jem]

I guess I'll go with the Hammond, the 125ESE is 15W?

It's getting comfortably confusing as I get closer to ordering.

It's getting confusing because you're making it harder than it has to be.
...
Hammond makes a line of single ended transformers, the 125ESE is their top specification SE in the 125 series. The 125ESE is a 25 watt transformer so it will work with nearly any tube you might want to use in the future. It's more transformer than you really need.

Actually the 125ESE is the 15 watt, the 125FSE is the 20 watt and the 125GSE is the 25 watt version.

http://www.hammondmfg.com/125SE.htm

[utervo]

Thanks for those, perhaps I'll put all the options on differents jacks.

I've been drawing the layout today and I am wondering why in the Ceriatone layout the pins 7 & 8 and 2 &8 on the 6v6 have been connected togeth via 100ohm resistor?

[davent]

Thanks for those, perhaps I'll put all the options on differents jacks.

I've been drawing the layout today and I am wondering why in the Ceriatone layout the pins 7 & 8 and 2 &8 on the 6v6 have been connected togeth via 100ohm resistor?

Hello,

It's the pseudo centre tap for the filament winding of the PT. Pin 8 is the cathode, pins 2&7 the heaters. You could run the 100r resistors from pins 2&7 to ground to create the centre tap or you could run them to a raised Vdc (eg. pin8) to create the centre tap and reduce hum from the heater supply. Using the raised Vdc is said to offer the better performance.

dave

Edit; Should add, if your PT filament winding has a centre tap connect it to pin8 of the 6v6 instead of ground, eliminate the 100r resistors. You'll achieve the better hum reduction.