Search found 2606 matches

by Andy Le Blanc
Mon Jul 10, 2023 3:01 pm
Forum: Technical Discussion
Topic: cold clipper
Replies: 13
Views: 1609

Re: cold clipper

I appreciate the statement about local feed back, stability and a cold clipper. In some jcm 800 bass amps, a 10k biased stage is used very early in the pre for stability. De-generation is useful.
by Andy Le Blanc
Sat Jul 08, 2023 3:00 pm
Forum: Technical Discussion
Topic: 70s Fender Bassman 100 Head Sounds Harsh
Replies: 21
Views: 1311

Re: 70s Fender Bassman 100 Head Sounds Harsh

If the rig was run with no load, your gonna have to start with the power supply and the power side of the amp. You can isolate the input of the phase invertor, grounded to check static conditions, or as a signal input to isolate the power side for testing, signal thru and O-scope analysis. Scrutiniz...
by Andy Le Blanc
Wed May 17, 2023 1:47 pm
Forum: Technical Discussion
Topic: Single ended EL34 amp design
Replies: 127
Views: 6665

Re: Single ended EL34 amp design

El34/el84 are power pentodes, verses 6l6/6v6 which are beam power tubes. The "knee" that optimizes power output curves with the beam tubes has a tone character that is different than the older power pentodes. In general terms, if you mind the limitations of your available parts, like the max heater ...
by Andy Le Blanc
Thu Mar 23, 2023 11:40 pm
Forum: Technical Discussion
Topic: OPT driven reverb into second amp input
Replies: 8
Views: 798

Re: OPT driven reverb into second amp input

Thats an echo jet. Its a "F" type verb tank, the Input from the speaker + is a RC filter, 300 to 1k paralleled by a large value 50uf (you can play with the value) non-polar cap. You can plug the out put into any thing, any second amp. I've built that one. Fun to gig with, the effect is more of a "di...
by Andy Le Blanc
Sun Sep 11, 2022 10:08 pm
Forum: Technical Discussion
Topic: Disbalancing paraphase inverter?
Replies: 22
Views: 2368

Re: Disbalancing paraphase inverter?

LTP are self balancing, they hold up well and maintain balance, as the tube ages and the dynamic characteristics drift. Paraphase invertors are actually harder to maintain a good balance, the balance changes with gain. The harder you hit it, the more the balance drifts. Remember the basic requiremen...
by Andy Le Blanc
Sun May 15, 2022 1:44 pm
Forum: Technical Discussion
Topic: Amp shielding
Replies: 7
Views: 1110

Re: Amp shielding

I found issues with how the input is grounded, and wire dress, the actual physical wire lay in the chassis, was more important than adding extra shielding. Inside the chassis, some points in the layout are prone to capacitive coupling, long grid wires. Sometimes the choice of wire in a build will in...
by Andy Le Blanc
Mon May 09, 2022 3:14 am
Forum: Technical Discussion
Topic: Power tube output transformer mismatch
Replies: 21
Views: 3250

Re: Power tube output transformer mismatch

Exclude the tube for the moment, and look at the PT and the OPT. The transformer set has its own limiting specifications. The power transformer has a ma. rating for the voltage it provides, and the output transformer has a max primary DC bias ma. rating. Both need to be respected as a limit for your...
by Andy Le Blanc
Fri Mar 25, 2022 5:10 pm
Forum: Technical Discussion
Topic: Tube preamp pedal output impedance
Replies: 4
Views: 823

Re: Tube preamp pedal output impedance

matching transformer
by Andy Le Blanc
Fri Mar 25, 2022 3:00 pm
Forum: Technical Discussion
Topic: Got lucky and got some tubes
Replies: 4
Views: 765

Re: Got lucky and got some tubes

That is a piece of happy. Yup,... I keep my eye's out for old US tubes. Even so far as abandoned TV's in forgotten junk piles in the woods. Having a N. American MFG with an eye towards overall quality is enticing. The Russian stock is/was sometimes pretty good with the commonly consumed tube types, ...
by Andy Le Blanc
Thu Mar 24, 2022 7:32 pm
Forum: Technical Discussion
Topic: Got lucky and got some tubes
Replies: 4
Views: 765

Got lucky and got some tubes

Its a mad house, a mad house,... I got a pair of Tung-Sol EL34B. Totally not expecting the crush and demand. I had to source them in Canada. Every supplier is out of stock and swamped,... Holy Moly So,... New production Tung-Sol EL34B What are your experiences with the current Tung-Sol brand and the...
by Andy Le Blanc
Wed Feb 09, 2022 3:37 pm
Forum: Technical Discussion
Topic: Best way to start learning about amps? And in what order?
Replies: 9
Views: 1404

Re: Best way to start learning about amps? And in what order?

Second that,.. I started before the web,... it was beg bum borrow and steal the informational resources. The more informational resources the better. But, ultimately I pulled together a box of junk and built an amp. Get an iron, a multi-meter, a signal generator and an O-scope. Non of it has to be t...
by Andy Le Blanc
Wed Feb 09, 2022 3:18 pm
Forum: Technical Discussion
Topic: Fender Blues Jr IV: crackling noise -> no sound
Replies: 15
Views: 1574

Re: Fender Blues Jr IV: crackling noise -> contact cleaner -> no sound

spray out the the controls with a good contact or wire harness cleaner, but make sure you re-lubricate the controls with a control/contact /lubricant. I been in too many of those for the same issue for bad resistors in the signal path. Once you re-establish signal thru you can "chop stick" the compo...
by Andy Le Blanc
Wed Feb 09, 2022 2:55 pm
Forum: Technical Discussion
Topic: 12V to 250V schematic? (Tube in pedal platform)
Replies: 5
Views: 1282

Re: 12V to 250V schematic? (Tube in pedal platform)

Back to back 12v/120v transformers. A 12v ac wall wort (120v to 12v) externally with sufficient ma. 12v to 120v internally with a voltage doubler.
From DC you could run a chopper. Old school, just like an old car radio, step up to the required B+.
by Andy Le Blanc
Mon Jan 03, 2022 1:57 pm
Forum: Technical Discussion
Topic: 12AX7 test power supply
Replies: 15
Views: 1134

Re: 12AX7 test power supply

You can use a single 12ax7/12at7/12au7 as an adjustable voltage regulator. You'll lose around 50v off the top, with the insertion loss, and a gain a usable voltage range. Simple circuit, tube/socket, a 100r and a 10k ww pot. Has around 5w capacity. From there you can step up the watts by using a pen...
by Andy Le Blanc
Fri Dec 31, 2021 6:51 pm
Forum: Technical Discussion
Topic: Phase Inverter Choices
Replies: 16
Views: 2458

Re: Phase Inverter Choices

LTP came out the need for stability, from oscilloscopes. Self stabilizing and resistant to tube characteristic changes that come with age. Solid, but it operates using feedback, and it cancels even order harmonic distortion. They can sound a bit "hard" or "cold". Good thing is that you can be critic...