Modified tone stack on 5e3

[Gerard]

Has anyone built this amp? just wondering if the tone stack sounded good. I have most of the parts to build this and was wondering how it sounded. I already have built a Mission 5e3 (all stock), so I was looking for something a little different. I love the 6v6 tubes!! I would like to do fixed bias and solid state rectification. Any thought comments or suggestions?

Also what do the 470R resistors do on pins 4 and 6 of the output tubes ? Should I increase the filter caps also?

[RWood]

what do the 470R resistors do on pins 4 and 6 of the output tubes ?

Can't help you with the sound of that circuit but the 470Rs are the screen resistors. They use pin 6 as a tie point before sending the screen B+ to pin 4.

On the layout that "b" on pin 4 should be next to pin 6, because that is where the B+ comes in. If you connect "b" to pin 4 you are bypassing the screen resistors and the amp will work but you don't get the benefit of the 470Rs.

RWood

[fyl]

Looks like the S2 Amps version of the Tweed Deluxe. It basically sounds like a tighter 5E3, with a real bright channel and way less interaction between volume & tone, 6G3-style.

If you fancy old style or NOS 6V6GT's, you should replace the 250R with a 300R or 330R if your PT puts out more than 300V loaded; no problemo with JJ's.

Filtering caps should be rated for 500V with a modern PT - loaded voltages are AOK but you can get more than 470V unloaded.

I'd further defart the amp by lowering the post-PI coupling caps from 100n to 47n or even 22n if you play with high output pups.

Adding a 330K resistor between the cathodyne 1M and V2 pin 7 is a boon if you play modern style and crank the amp to stage levels. No more farting/blocking.

You may also consider splitting the 22K dropping R using say 18K and 4K7 and adding a fourth filter cap (C1: V3 & V4 plates, C2: V3 & V4 screens, C3: V2, C4: V1). Better response, less noise.

Filtering can also be improved by using 33/22/22(/22) µF. I wouldn't go above 33µF with a vintage 5Y3GT and a standard PT.

Oh, and don't forget to raise heaters, either thru a dedicated voltage divider or by connecting the PT 6V3 center tap to the top of the power tubes cathode R. The cathodyne can be quite hard to modern 12AX7's - particularly those of Russian manufacture - because of the heater to cathode voltage diff, reducing it is a Good Thing™ (and also reduces heater-induced hum).

[Gerard]

Thanks RWood and fyl for your input. All good tips to remember. I always like to post questions before I start to build: I will defart this amp using your suggestions.
I am wondering now if I should use 6l6 tubes, I plan on using a solid state rectifier with a 300-0-300 PT? I would like more punch, and all my other amps are cathode biased, Any thoughts?
Thanks again.!

[fyl]

6L6's => 5 to 6K pri OT and 10W cathode resistor.