Hybrid Tweed Tremolux/Brown Deluxe

[Bruce / Mission Amps]

Thanks Bruce

I've revised the schematic again (3c).

1) Re: the plate for the 2nd stage, I will do what you suggest but perhpas add a 4k7-15k resistor in series with the 'output' of the 100k trimpot so that I can get more plate resistance dialed in in the 'input' side.

2) Re: the voltage divider to the grid of the 2nd stage - not sure if I should go as low as 220k to ground but maybe I could start with 1M (and then if that's no good 470k etc)

3) Re: the resistors in the PI, I have amended them to your suggested ranges, but maybe will leave the NFB at 56k (or possibly less). I will leave the 1k5 resistor to ground as per the 6G3 schematic

4) Re: the voltages - I will try and get the voltages down, perhaps with an EH 5U4GB I have (which seems to pump out less than the Sovtek 5U4G). My other option would be to drop one of those 20uF in parallel at the filter reservoir. But I don't think a 5Y3GT would have enough lemons. (and then there's aways zeners)

Cheers

1. I don't think you'll need that 4k7-15K dropping resistor but if you do, it wouldn't hurt to shunt the B+ to ground with an 8uF-10uF -450v cap after it not before it.
Use a single 22uF to 33uF 500v cap for the main first filter cap and slide your extra 20uF over to where your 10uF cap is now.

2. If you have room, use a 1M pot wired as a variable resistor.

3. Use a 20K resistor with a 50K pot wired as a pot for variable NFB and pick what sounds good.

4. With 6V6s I think you'll like a NOS 5Y3GT but a Russian 5Y3GT is not a 5Y3, it is actually more like a GZ30 5u4c (Euro 5V4G) and the B+ will be higher... nut, since you have a negative voltage bias supply here... make the bias voltage variable enough so you can bias any pair of 6V6s or 6L6s at around 55% to 70% of the power tube rating.

[tubeswell]

Cheers Bruce

See 3d - is that what you mean't by inserting a 10uF decoupling cap?

[tubeswell]

Actually I just thought of another option for stage 2. I suppose that'd work as well (be less caps cluttering up the place)

[Bruce / Mission Amps]

Actually I just thought of another option for stage 2. I suppose that'd work as well (be less caps cluttering up the place)

Yes this is good... you could probably just as well use two smaller 10uF-450v caps for the final two in the B+ rail.
I'd still consider using a 33uF-500v cap for the main filter though.
A 5Y3GT will run for years with a 30uF cap regardless of what you might have heard from others.
If you are worried about it though, use a 2 watt, 10ohm to 22ohm resistor right after the rectifier's cathode lug to feed the entire B+ rail.


Added:
Oops... I just looked at the preamp triode insert again.
The wiper tied across the 4k7-15K resistor defeats it completely... I wouldn't do that one.

[tubeswell]

Thanks a million Bruce

I am working up a layout for this which I'll post in a few days. (Its a goer, but I've got temporarily distracted)

Cheers

:-)

[tubeswell]

Finalish (theoretical) Schematic & Layout

Okay then, finished twiddling with paper, I've got (what I think is) the prototype pretty much theoretically figured, now for the real-world (when I get time in between my 6G15 build) ;-)

Just a couple of my own remarks: -

I'm kinda figuring that the trimpots (except for the bias one) will get replaced by permanent resistors once I settle down to a groove. I'l start out with building a 12AY7 Stage tho' (using 100k Plate, 820R common cathode bypassed V1 - even tho I've got it drawn the other way on the layout (and the layout title bar says '3d' when its meant to say '3e' -Ooops).

Where I've got the 10uF decoupling cap from the V2 plate resistor - Is that going to be okay locality-wise (d'y' think) - don't think'll do any harm myself? The pre-amp decouping caps'll get grounded with the pre-amp grounds.

I don't have the Jsch layout programme (cos I dunno where to find it) so I did the layout diagram using the schematic programme

My profound and heartfelt thanks to everyone here for your contributions

Cheers

[txstrat]

Hi TW,

I don't think the filter cap (10uF) in between the plate resistors of V2 would be necessary, cause you are filtering with the 20uF in the B+ line already.
The two resistors are to be seen as one load for the plate with a different load to the coupling cap (.01-.022) due to gain.

Matt

[tubeswell]

I hear what you're saying txstrat, however Bruce recommended it as a further decoupling cap, so I thought I'd give it a try. I understand that he thought it adviseable if I was going to use a pot in place of the 100k. (On the other hand, I could just build it without that trimpot and experiment with changing the plate/split load resistor values - but the trimpot would make it a bit easier to find the G-spot).

[Bruce / Mission Amps]

Since space is an issue and the loading on the B+ rail is light after the screen node, I would use all 10uf caps for the last three filter caps instead of two 20uF and a single 10uF on the new node. That should be good enough for good filtering and audio decoupling.
So, it would be, power tube's plate and screen node having a 20uF each, with the following B+ nodes using the 10uF/450v caps.
***************

Also, I think you'll find that the .003uF cap across the plate load resistor will dull the preamp WAY too much high frequency snubbing.
I wouldn't use more then 1000pF and that would be only if I really needed it.

[deci belle]

Though I'm quite late to this game tubeswell, I've found myself stumbling into this same circuit combination, mainly due to the similar B+ rail values and tone criteria. Another factor is the size of the 5G9's cab— which seems juuuust right!

I recently wriggled through the LTP gain issue through no fault of my own (thanks to great people hanging out on this forum).

I have the volume/tone pots separate for each channel (in my layout) cuz I'm working with the larger chassis, is the main difference.

Thank you for the well-refined documents, tubeswell— I'll be studying these!!

[tubeswell]

Arrggghh! An old thread. I prefer the stock circuit of either type of amp to the hybrid idea. It was a rather pointless exercise.

[deci belle]

haha!! It's true, and I'm ready for that, tubeswell. Remember how Bruce et al were hot-rodding the 5e3 and now you'd never know it by hearing them (like you) talk about doing just that nowadays?

Mine started out a hybrid 5 years ago and it's just helping me work out experiments as a mule should. We have to go through these logical machinations… Actually, this round is helping me to decide which one to build next as a straight circuit.

Don't be so embarrassed!! Ok, well, go ahead (because I copied your switchable bias circuit in the process~ hehe), and Pete just helped me build the switchable PI circuit!!

It sounds great all four ways— but certainly, it's (pointless, as you say, and) hardly worthy of any of the original circuits standing on their own~ but I'm a novice, and besides, I don't actually know how to play electric guitar so much (as you do) …it's too hard to learn and play songs all the way through! I can build an amp without even understanding why it works (kinda like those housewives did for Leo in Fullerton back in the day, eh?).