Trutone Stereo amp

[angelodp]

Got it.

On another front. When I run the amp at 95v-100v, the hum is greatly reduced. At higher voltage I do get 120 and 60 cycle hum. Would it be helpful to add additional diodes to the rectification? The gain and volume of the amp is now greatly increased with the Fender pre-amp stage.

[sluckey]

Would it be helpful to add additional diodes to the rectification?

no

[angelodp]

Ok, so any hints on what I can do to address the hum levels. Electrolytic Caps have been changed, no DC on coupling caps, Voltages are within range. Have a handful of Tubes now and selected the two most quiet tubes.
As I said, with the amp at lower voltage and with the bottom plate in place its close to 'quiet enough'.

thanks A

[sluckey]

Divide and conquer. Put a ground on V6A grid. Hum stays, check power amp. Hum gone, check preamp.

[angelodp]

Got it.... (thanks Steve G - a pal). Turns out with the two stages of gain from the 12ax7, then into the ECL86 first triode (that's more gain..... way too much gain), then into the PI..... that had the amp major humming and volume went way high at 2 1/2. I jumped across the first gain stage of the 12ax7 directly after the volume output of the tone stack through the .047cap into the grid of the ECL86.... presto chango, amp now has no hum and plenty of volume and breakup at 6-7 on volume. I did also elevate the heaters to cathode of the power tube and reconnected some NFB. Plan on putting a variable NFB now. Tone stack quite responsive and bright switch works swell. All in all now a rock amp.

My hint came from running the amp at 90v which was helping. Then Steve G recommended lowering gain and removing one stage in preamp.

Thanks for your interest, prodding and intel.

[angelodp]

Update, it blew up.... just kidding. It is now a full blown Stereo guitar amp. I implemented the B side with a
Tweed tone stack for now, might change that out. It does have a big mid bass on the B side and Marshally treble feel on the A side (which has NFB control). With the two signals combined using the ABY from Radial it is quite dynamic. Yet to try a wet/dry thing, but its does not hum and no replating and wellll.... its good.

Thanks Guys

[angelodp]

Hi, scored a couple more ECL86 tubes. I swapped out the Tweed tone-stack for a more Marshall style. Amps plays well as single side at a time. It also plays well in stereo through the radial box, for about twenty minutes, until the tubes have warmed quite a bit and then the hum level increase somewhat. I suppose silencing this amp would be an extra labor for love, as the older R's have likely drifted and the Coupling caps and bypass caps are older.

I do have a question. Would this circuit sustain a cold clipper stage with a gain pot to take the gain and distortion to the next level.

Ok, I did tack in the cold clipper, 10k on K, .047 coupler, 100k plate, 500k gain pot, as a new V1 then sending that to the
next stage which is just before the tone-stack. I see where Rob R has a colder clipper switch and Soldano uses a 33k for the clipper.

Moved Cold Clipper stage to after the Tone-stack. Much better result with a marked decrease in hum from its previous position. This is adding headroom and at the upper vol. levels it goes into a nice OD breakup. Now to find a good spot for the CC Master pot.

[angelodp]

Moving along, I am working on increasing earlier breakup. Right now with the Airbrake on and the amp dimed it is quite the little beast. I would like to eke out a bit more distortion, not gain, without the airbrake.

[angelodp]

Onward. Now have a bright cap 250pf on the B side. The A side has a switchable cathode bias (Cold & Hot).

What you see is a bit temp as I move some elements to the front (K -switch). Its been fun and I learned some new stuff.

I am contemplating a one tube reverb. Why...why not. This a mule-ish build to learn stuff and so far so good.
Its gone from dead to major hum to playable to now kinda interesting. Its a knob fest for sure. I recall Colossal talking about early builds bristling with knobs and switches and how all that went away as the tone quest became more defined. I have tons and tons to learn and I do intend to make progress in that regard.

Question, would this PT OT sustain a reverb circuit? I do have another tube slot to play with.

A

[angelodp]

Guys, this thing has an old fashion slide on/off switch?? Would you recommend replacing that with a more robust switch?

[sluckey]

I like slide switches. Hate building the little rectangular holes though.

[angelodp]

Ok so you don't see any over-arching safety issues with this style switch.... it works, does not arc. I do hear a bit of a pop when shutting down.

[angelodp]

Quick question on this amp. It's working nicely. I do have an interesting little hum from the PT that when I put my palm on it and press down goes away. Mind you it's not a case of simply touch it, it's with a gentle downward pressure that the low level hum goes away. I am thinking that some thin rubber washers might do the trick. I will have to move a Cathode ground, for the power tubes away from the PT bolt I am using.

Has anyone encountered this issue and solved it this way.

thanks A

[johnnyreece]

Sorry, I've not followed this project from the beginning, so I don't know what your PT looks like (disclaimer out of the way). This sounds a lot like mechanical PT hum, and as such, might you be able to fix it just by tightening the PT bolts?

[angelodp]

Hi, I did try that and they are super snug. It's funny but the minor vibration goes away when I press down with my palm. I tried re-orienting the OT's as much as I could but that had no effect. My thought is very thin silicon washers to dampen the unit.