New Build Ideas/ Suggestions??

[mauiboy81]

Hi guys..... It's been a while and I've missed you all

I have some Iron lying around that I am itching to make sing and I thought I'd see what you guys thought.

OT is a Mercury Magnetics Tweed Pro.
PT is an old thing salvaged from a 60's executone.

I figured I could build a single channel 5e5 or 5e5a Pro possibly with "vibrato" but that seems a little boring to me. I've built a 5e5a and a 5e3 before and although amazing sounding amps I wanted to try something new.

So what I've been thinking about is a single channel 5f6a preamp and pi into Cathode biased 5881 with adjustable or switchable or no NFB.

The Tweed Pro OT is not very beefy.
The Executone ran a 5u4GB 2-12au7, 1-12ax7, and 2-6l6

What do you think?

[mauiboy81]

This is the schematic from the executone that the PT came from.
Sorry for the large file... I had a hard time seeing it otherwise.

[Zippy]

So what I've been thinking about is a single channel 5f6a preamp and pi into Cathode biased 5881 with adjustable or switchable or no NFB.

Oh, you mean an octal Rocket!

Go for it.

[mauiboy81]

I do want to build an octal rocket and will do a more proper one soon. This build is partly to test the waters. I just don't know how it will be with the wimpy OT.

[M Fowler]

The octal Rocket is a great platform just like the 5f6a. Take a look at some of the David Allen amps layouts he has a great selection of circuits you could try and sound great as well. Hot Fudge with nuts for example.

Mark

[mauiboy81]

Is it possible in a 5f6a (jtm45, ac30, rocket) style amp with CF tone stack to add a switch off the volume wiper to coneect directly to the PI entrance so as to bypass the extra gain and CF tone stack stages? Kinda like an ac30 normal channel?


Also, to make the 5f6a NFB adjustable/switchable could I just use a switchable pot in series with a smaller nfb resistor? Would I need to do anything with the presence control components? I wouldn't want a presence control at all.

[chopstuck]

I have an old TV Pro 5A5 and need an output transformer. I was thinking about a MM but they want too much new.

I have scads of different OT's from old 6L6 Fender iron to big organ output and power trannys and some smaller 15 watt 7-8K stuff.

I would make you a good deal, really, to get a beeffier OT if that's what you want. Just PM me.

Shipping is cheap even from HI in a USPS " anything fits" box.

Marc

[M Fowler]

Mauiboy,

Henry H. from Redplate discussed that a while ago and has that feature in my Blackverb basic amp. Switchable presence.

Also the tone stack lift can be added to the 5f6a yes.

Mark

[mauiboy81]

Thanks!

I looked for that discussion but couldn't find it.
I'm not sure I understand the drawing... When the switch is on does it connect above the 1k resistor? If so that would put the 2k pot and 1k resistor in parallel?
What if I were to go with a variable feedback resistor and not presence control..... How would that look?

Thanks again,
Nick

[rp]

My 5F6A has a cathode / fixed bias switch. If you are building for playing out gigging the fixed bias is better IMO. If you are playing at home or recording the cathode bias is real nice and twangy-bouncy. I have limited experience in this but I don't think I like cathode bias on big amps played loud, I like the slam of fixed bias. You might want to consider a switch or leave yourself room to convert it to fixed in the future. Not sure about a 5F6A w/o NFB either but I never tried it, it makes a plenty big racket as it it. Maybe if it's going to be no NFB and cathode bias you might want to keep it around 370V and bias it hot. The Tweed Pro OT should be fine then.

[M Fowler]

Nick maybe Henry will comment about his circuit but I drew a layout attached the way I see it.

Mark

[mauiboy81]

Any idea how to wire it with no presence control? I'm looking for adjustable NFB with no presence control.

Thanks again!

Nick