2 questions about my Eico HF-20 conversion

[Foxfire]

1. i'm curious as to why (as per the schematic) the Screen voltages are higher than the Plates? the amps sounds good as it is, i'm just curious...

2. What are some clever things to do with parallel stages? i gutted the eico back to the power tubes and rebuilt it as a first version Sunn Model T. i only have a single input wired up as the "both" jack (bright and normal) in the Model T. as i said above i like the sound of the amp but i feel like i'm wasting a stage here. Would tuning the 2 stages even more differently then they are (birght/normal) add "depth" to the amps sound? more gain would be fine but more depth would be cooler...i haven't found a whole lot of amps designed around parallel input stages so i'm either not looking hard enough or they are better ways to design an amp.

Thanks...

[Jazz P Bass]

The screen at a higher potential, through the opt, tells me it is an ultralinear setup.
http://music-electronics-forum.com/t28949/

[Foxfire]

yes it is and i had a suspicion that it had something to do with it being ultralinear so i searched out schematics of other amps and wasn't able to find any with screens>plate so i had some doubt.

[Tage]

Well if you have it wired like a Old Model t then you could consider biasing each stage separately, a very good example of that would be Marshall JMP's, the bright and normal channels are biased differently, the bright channel using a smaller bypass capacitor to achieve a treble boost. mixing the two channels has been done often and in my experience can be used to add more "depth."

http://www.drtube.com/schematics/marshall/1959u.gif

If you haven't already you should read merlins article on preamps. It goes over the effects of different bypass capacitors and differing bias and their effects on clipping.

Valve Wizard - How to design valve guitar amplifiers

You never know what interesting combinations will provide a unique effect together, especially when they have there own volume controls.

I hope this is helpful for you, good luck with any changes you make.

[Gingertube]

I did a conversion of an old PA Amp into a Guitar Amp.
Here is the "Trainwreckish" Preamp Section I used - it is basically the A0 Trainwreck preamp circuit which is scattered around the web with my own mod for a parallel input stage. Note the different operating points (bias point) on the two triodes, with different bypass caps, I thought it gave some nice harmonic emphasis.
Big label on the front of the old chassis proclaiming it to be a "Junkbox Trainwreck"
Cheers,
Ian

[Foxfire]

thank you everyone so far, i have some reading and soldering to do...