Still no break-up. 2x 5F1's.

[Dave H]

Dave H-

So wouldnt I be killing 2 birds with one stone with this suggestion?

Yep, the only caveat is finding somewhere to mount the components.

[Jazz P Bass]

They added an RC filter for the screen. That won't reduce the B+ voltage. I was thinking of a pi filter before the OT like the one in the 5D2 Princeton.

The 47 ohm resistor is the bottom resistor of the feedback divider. It will have more gain like that (less -ve feedback). The 5F1 uses the 1k5 bias resistor as the bottom resistor of the feedback divider.

Princeton 5D2.

[loudthud]

The contemporary crop of tubes branded as 5Y3 have lower voltage drop than the traditional ones from the 60's. If you can find a NOS 5Y3, it will lower the B+ some.

What do you have for a 12AX7? Have you tried any other tubes?

[Sea Chief]

The contemporary crop of tubes branded as 5Y3 have lower voltage drop than the traditional ones from the 60's. If you can find a NOS 5Y3, it will lower the B+ some.

What do you have for a 12AX7? Have you tried any other tubes?

Not yet. At the mo its a generic sovtek 12ax7, as is the 5y3. The sound is quite hard and unforgiving and not too inspiring but how much of that is due to these tubes I cant begin to tell, or have enough experience yet of tubes to know. How much is a NOS 5Y3, and a better 12AX7?

Its great I can start thinking on these lines now- what a relief.

[Sea Chief]

Since we're talking mods...

A bit conscientious, but a twisted filament circuit with a filament center tap lead to the top of the 6V6 cathode circuit can virtually eliminate hum in these amps IMHE.

I'm all for adding a "sag" resistor as part of a Pi filter as per Dave H.

Raising the preamp voltages, as per Jazz's post will also provide more drive for the power tube grid, increasing clipping.

The added sag resistor and power tube grid resistor will also reduce the harshness.

Another idea might be a "conjunctive filter". Which is just a fancy term for a resistor and capacitor circuit across the OT primary leads. The right component values can really smooth out the tone without making the amp dull sounding.

Fine tuning these little amps can be confusing for a novice. We've done this crap for years. If you're up for it there's every possibility of idealizing the tone for clipping.

Lots of suggestions coming.. its all a bit overwhelming tbh I dont know my oorse from me elbow. How do you higher the preamp voltage then? sounds like upping the gain here makes sense if I can. I like the idea of the 'added sag resistor and power tube grid resisitor' to take off a bit of harsh too, although Ive absolutely no idea what it means but it sounds good!

[hylaphone]

Easiest to try a vintage 5Y3 rectifier first, might make a dramatic difference -
Just find a tested used one for a few bucks, it's a common tube... if you like the sounds then stock up!

[eschertron]

GROWL is good! I prefer less NFB - up to none at all - on the champ amps I've played around with.

Princeton 5D2.

[SNARK]With the screen on the same node as the preamp, and the grid-leak bias, I'm supposing this wasn't one of the most popular models...[/SNARK]

But I recognize the Pi filter here (before the B+ node) as a way to get ripple out of the power tube, true that. Good call.

[Dave H]

Yep, the only caveat is finding somewhere to mount the components.

Sea Chief,

A simpler way to reduce the B+ voltage would be to replace the wire between pin 8 of the 5Y3 and first filter cap on the board with a 470 ohm 7W resistor (Maplin). It would only take a few minutes to do and it should fit in just fine. Just make sure the wire to the OT is connected to the first filter cap and not pin 8 of the 5Y3. On your picture it looks like it could be connected to pin 8 via a link to pin 7.

[Chuck H]

Since Sea Chief isn't a tech I'm thinking it might be easiest for him if we just used his photos and painted red arrows on them with instructions. Or something like that. No one wants to be the bomb squad guy wondering which wire to cut

[Enzo]

Jazz. Regards NFB and related from an earlier post. Note the feedback resistor in the 600 is 2.2k, not 22k as in the 5E1 and 5F1.

I think when comparing the Champion 600 and the older Champs, you need to include both 5E1 and 5F1. 5E1 has the choke on all B+. the 5F1 got rid of the choke. Notice the 5F1 removed the cathode bypass on the input stage, probably to back off the gain some. Maybe the amp was breaking up too easily.

Now on the 600 Champion, the input stage bypass has returned and they even bypassed the second stage, so the amp now has lots of gain, tastes have changed. But on the old models, NFB went into the cathode of the middle triode. But a bypass cap will bypass NFB as easily as it bypasses any other audio. SO they bypassed only the cathode resistor, and added a 47 ohm to ground to provide NFB injection but still allowing stage bypass. The old NFB was 22k/1.5k. but to get that same level would have required another 1.5k under the existing one. So to make levels equivalent they lowered the feedback resistor to 2.2k and the tail resistor to 47 ohms.

[Sea Chief]

Sea Chief,

A simpler way to reduce the B+ voltage would be to replace the wire between pin 8 of the 5Y3 and first filter cap on the board with a 470 ohm 7W resistor (Maplin). It would only take a few minutes to do and it should fit in just fine. Just make sure the wire to the OT is connected to the first filter cap and not pin 8 of the 5Y3. On your picture it looks like it could be connected to pin 8 via a link to pin 7.

That sounds good Dave H. I have a 470r 10w.. any good? I guess will act as a bigger 'heat sink' if thats the idea, but will its bigger size remove more V? My noggin say no.

I can remove the white wire from rec pin 8, leaving it from the the 1st filter cap, and switch it over to pin 7 of the rec (IE used as a junction only, to connect the OT as it is already here/ remove the link to pin 8 of course). Then put the R fatso in between 1st filter cap/ with the white wire as it is, and rec pin 8.

Is that sort of the right way of thinking to do such an addition?

[cobbled together? the very cheek!)

[Jazz P Bass]

[cobbled together? the very cheek!)

Well, now I must apologize for that statement.
It is rather a nice build.

[Chuck H]

Sea Chief,

With the feedback resistor gone you can now bypass the second preamp cathode for a lot more gain. Use a 2.2uf to 22uf electrolytic capacitor with a voltage rating 10V or higher. Add it parallel to the circled resistor with the negative end toward ground.

[Sea Chief]

Well, now I must apologize for that statement.
It is rather a nice build.

hehe! I didnt make it anyway.

[Sea Chief]

Sea Chief,

With the feedback resistor gone you can now bypass the second preamp cathode for a lot more gain. Use a 2.2uf to 22uf electrolytic capacitor with a voltage rating 10V or higher. Add it parallel to the circled resistor with the negative end toward ground.

Ah ok I could do this in a jiffy. Neg twds top of pic then.

Can you tell me if my 10w 470r resistor is any good? (and my method of fitting #206 is not madness)?