Search found 39 matches

by voskarp
Mon May 25, 2020 1:04 pm
Forum: Technical Discussion
Topic: Why do I get this spontaneous Tremolo? (And how to get rid of it?)
Replies: 11
Views: 733

Re: Why do I get this spontaneous Tremolo? (And how to get rid of it?)

I moved the EF86 power supply to B+3 (and changed R25 to 10k), and voilà! -tremolo effect gone!

I'm glad I could solve this without tearing the whole amp apart! :D
by voskarp
Sun May 24, 2020 12:46 pm
Forum: Technical Discussion
Topic: Why do I get this spontaneous Tremolo? (And how to get rid of it?)
Replies: 11
Views: 733

Re: Why do I get this spontaneous Tremolo? (And how to get rid of it?)

I reduced the resistors to get higher voltages at the valve plates, I found them to low.

The PT is from an AC4C1 with a top boost circuit, so it used to power two ECC83s and an EL84.
by voskarp
Sun May 24, 2020 12:27 pm
Forum: Technical Discussion
Topic: Why do I get this spontaneous Tremolo? (And how to get rid of it?)
Replies: 11
Views: 733

Re: Why do I get this spontaneous Tremolo? (And how to get rid of it?)

Yes, that could be it. I guess I should reduce R25 then.
by voskarp
Sun May 24, 2020 11:20 am
Forum: Technical Discussion
Topic: Why do I get this spontaneous Tremolo? (And how to get rid of it?)
Replies: 11
Views: 733

Re: Why do I get this spontaneous Tremolo? (And how to get rid of it?)

It occurs when the volume (gain) is more or less maxed, but the signal from the guitar is fading. (As in the sound sample).
by voskarp
Sun May 24, 2020 10:18 am
Forum: Technical Discussion
Topic: Why do I get this spontaneous Tremolo? (And how to get rid of it?)
Replies: 11
Views: 733

Re: Why do I get this spontaneous Tremolo? (And how to get rid of it?)

If it was the power transformer, there would be sag at max signal, but this effect comes quite opposite when the signal wanes.
by voskarp
Sun May 24, 2020 8:44 am
Forum: Technical Discussion
Topic: Why do I get this spontaneous Tremolo? (And how to get rid of it?)
Replies: 11
Views: 733

Why do I get this spontaneous Tremolo? (And how to get rid of it?)

This homemade "AC4" where I've combined the preamps from two different amps has a weird quirk. When the volume knob of the EF86 channel is set over 3/4 a tremolo effect starts to set in as the note fades (sample 1). Sample 2 is playing though channel two (ECC83) at low volume, with the EF86 channel ...
by voskarp
Sun May 03, 2020 5:29 pm
Forum: Vox/Hiwatt Discussion
Topic: AC4 project
Replies: 27
Views: 6954

Re: AC4 project

I just tried the amp with a 12AY7, that I borrowed from the Tweed Deluxe, in V2. It works really good, I get a little clean sweep on the EF86 channel (about 1/5), then it starts overdriving slightly. The second channel is clean to about 1/3, and really starts overdriving at 1/2 volume. At full volum...
by voskarp
Sat May 02, 2020 9:27 am
Forum: Vox/Hiwatt Discussion
Topic: AC4 project
Replies: 27
Views: 6954

Re: AC4 project

Not a problem, I choose the direction! (Even though it might be wrong!!!) :D
by voskarp
Fri May 01, 2020 8:38 pm
Forum: Vox/Hiwatt Discussion
Topic: Pre '60 style TV front AC4 build
Replies: 36
Views: 11445

Re: Pre '60 style TV front AC4 clone

ChopSauce wrote: Fri May 01, 2020 12:41 pm Thanks for the suggestion! I'm not sure how a zinc-plated (mostly) screw will "take" the solder but that's an idea... 8)

My best B plan remains a solder eyelet screwed above a spacer, though.
Heat is the solution to everything (except soldering germanium transistors)
by voskarp
Fri May 01, 2020 8:31 pm
Forum: Vox/Hiwatt Discussion
Topic: AC4 project
Replies: 27
Views: 6954

Re: AC4 project

Honestly I'm kinda shooting in the dark, but I've read up on some stuff and get by with a little help from my friends... :) Here are some sound samples: Made some sound samples of my amp today. I used a free version of an app that only let you export 90 sec of sound, so some are cut at the end... I...
by voskarp
Fri May 01, 2020 10:31 am
Forum: Vox/Hiwatt Discussion
Topic: Pre '60 style TV front AC4 build
Replies: 36
Views: 11445

Re: Pre '60 style TV front AC4 clone

For the ground bus I think you could just use a small screw (like M3) and fasten it to the chassis with a nut and locking washer. Maybe use a small file and cut a notch in the top for the wire.
by voskarp
Mon Apr 20, 2020 3:54 am
Forum: Vox/Hiwatt Discussion
Topic: AC4 project
Replies: 27
Views: 6954

Re: AC4 project

OK, thanks. So as I understand it, it's safest to either bypass the 3k9 cathode resistor, or putting an extra cap between ch1 pots and mixing point.

I didn't explain that I referred to the AC4 (V1) schematic earlier in this thread, where the channels are mixed just before the EL84.
by voskarp
Sun Apr 19, 2020 6:22 pm
Forum: Vox/Hiwatt Discussion
Topic: AC4 project
Replies: 27
Views: 6954

Re: AC4 project

OK, I see. So there's no need to put an extra cap after the volume pot, like in the 2:nd channel? For clarity: the added channel is ch 1, but I want to move the mixing point so it's before V2b, instead of before the EL84, as in earlier schematics. I just find the resistors/caps in series arrangement...
by voskarp
Sun Apr 19, 2020 3:59 pm
Forum: Vox/Hiwatt Discussion
Topic: AC4 project
Replies: 27
Views: 6954

Re: AC4 project

It was this comment on TDPRI that made me realise there might be a problem with simply adding an other channel like in the schematic. TDPRICut.jpg My question as why the caps is more relating to the arrangement with two resistors and caps in series, and the 1M to the grid in between them, and not so...
by voskarp
Sun Apr 19, 2020 6:40 am
Forum: Vox/Hiwatt Discussion
Topic: AC4 project
Replies: 27
Views: 6954

Re: AC4 project

I have a question about this arrangement with the caps and resistors.
WhyThisArrangement.jpg
I wonder why it's there, and what it will mean for the mixing of channels before V2b instead of after.
AC4v.2.jpg