Snider Prototype (Traynor YGM-4)

[sonicmojo]

The hum persists even when I remove the .02 coupling cap pre-PI. If I remove the PI tube, hum all gone, even when I remove the extra 100uF filter cap. Would a ground loop act like this or do I have a PI problem? Different tubes change it but don't resolve.

I've tried a bigger choke and no help there.

[sonicmojo]

I elevated the heater supply artificial center tap to the power tube cathodes with not so much effect on the 120Hz hum, perhaps a little bit. I also implemented some slight negative feedback (1.6k) that helped reduce the hum significantly. In doing so, I realized my OT secondaries were reversed and may have been causing some other problems but I need to test further. I'll rework my preamp grounding scheme a bit tomorrow and hopefully that will kill some of the residual hum and I may rethink the negative feedback if that is the case but it is reasonably quiet now. I'm not so happy with the PPIMV single gang 1MA pot. It doesn't give much usable sweep. I may try a different scheme but in my version of this amp this circuit still sounds best bypassing the MV and just using gain and guitar volume to control things. still tweaking.....

[studiodunn]

Wish I had the technical prowess to add something here, but I don't. I have however owned 3 Sniders and everyone of them hummed.

I'm hoping you find a solution so I can look into implementing it into my 484.

[sonicmojo]

Wish I had the technical prowess to add something here, but I don't. I have however owned 3 Sniders and everyone of them hummed.

I'm hoping you find a solution so I can look into implementing it into my 484.

Hum reduction in these higher gain type amps is a give and take battle quite often.... Do you have any gut shots of your amp? I've never seen the inside of a production Snider. You could always add some negative feedback easily but would lose a little bit of something else in the process.

I'll have to compare to the original again. I can't remember if there was much hum in it or not.

I added a buss bar for the preamp and I didn't get any perceived improvement. It's possible I should have tried to keep the PI tube further away from the power tubes and but I didn't have the room for what I was trying to fit into this chassis. Not perfect but at an acceptable level of hum and of course some hiss when gain cranked. I may add a NFB defeat switch for fun when I want the full raw version.

Once I get more experimentation done with my amp, I may try a similar thing in a Princeton reverb chassis with 6V6s.

[studiodunn]

No gut shots, but I will get you one.

[sonicmojo]

Boxed up in the original Ampeg cabinet with 10" speaker. It is a mean little amp although a bit inefficient with the 10" speaker and ported cabinet. I can't tell much of a difference between the SS and tube rectification, even when swapping a few tubes. I'd like to increase the reverb a bit. I guess I'm wanting more lush reverb on tap. Does anyone have any suggestions based on the schematic what might be and easy fix here with 2 triodes available? Maybe I can insert the reverb into the circuit a different way instead of how it taps off the treble pot. Going to keep playing around with it for a while.......

[10thTx]

I guess I'm wanting more lush reverb on tap. Does anyone have any suggestions based on the schematic what might be and easy fix here with 2 triodes available? Maybe I can insert the reverb into the circuit a different way instead of how it taps off the treble pot.

I'd try this. You could use a 1m dwell pot instead of resistor.

There is quite a bit of info on "one tube reverbs" here: http://el34world.com/Forum/index.php?topic=7957.50 ............... including reply #69 that uses a 6BM8 tube.

With respect, 10thtx

[didit]

Hello --

Here is a worked & well explained design for capacitive coupled constant current 6BM8 reverb. Should be fairly clean drop-in replacement using the triode for recovery. Provided sound sample makes me happy.

10thtx: Seeing presumptively a minor error on latest schematic, with gain bright cap drawn as resistor?

Best .. Ian

[sonicmojo]

10thtx: Seeing presumptively a minor error on latest schematic, with gain bright cap drawn as resistor?

That's just an old schematic. 10thtx was just trying to point out the reverb area with it. To avoid confusion, I've put the most recent and updated schematic on the first post with the layout so it will always be at top instead of buried. Thanks for the references on the reverb. I'll be experimenting.

[didit]

Mea culpa. Tube from the constant current capacitive coupled reverb design was a 6GH8A. I'd breadboarded with readily available 6BM8. These are in production, unlike other most/all pentode/triode tubes.

[sonicmojo]

I've done some experimenting. I think I'm not going to get any improvement with changing resistor and cap values in the current setup (I tried). I've been experimenting with adding a transformer, Princeton Reverb variety, with the attached one tube scheme, so using a 9AB2C1B tank which has the same impedances as a Princeton Reverb tank, I'm getting more reverb.....wish I had another triode for the input side. I'm getting some screeching oscillation on high gain settings so I'll have to tweak things a bit more.....

Am I on the right track? I'm kinda wondering if my input and output mixing points in the circuit are ideal.

I have a couple of 6BM8 tubes. May try that next if I'm not happy in the end.

[10thTx]

You need a cap between RV and the dwell pot. Use something between 500p and .001. I usually use .001

You can also decrease the cathode resistor value and increase the cathode cap value to increase reverb.

With respect, 10thtx

[didit]

A 12DW7 would help push driver current, at some loss of gain. And should help somewhat in both transformer and capacitive coupled circuits. No substitute for dual 12AT7 or a decent pentode though.

Best .. Ian

[sonicmojo]

I'll experiment with cap values once I get the transformer in.

BTW, the weird oscillations I was getting had to do with a new set of JJ EL84s that I put in. I thought I had broken something else with the reverb experiments as my bias trem also got really weak to nonexistent and my voltages were dropped down a bit. I must have a bad new tube. I swapped them back out and will put the bad ones on my tester later to see what they read. I was pulling my hair out for a little while.....

[sonicmojo]

Reverb sounds about 50% stronger with the transformer. I am getting some squeal when the dwell is turned way up and bright is on. Would lowering the 1000pf entry cap help things or do I need to tone down the reverb driver gain a bit? it has a 1.5k/25uF cathode now. This amp is geared to be very bright in those first couple of stages. I could probably play with toning down the preamp a bit an maybe lowering the PI caps a bit downstream. But then again, I think this Snider circuit was built to cut through the mix and I'd hate to un-engineer it too much. That first tube slot is finicky in this design. I've found that some tubes simply don't play nice.