First amp build questions
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- martin manning
- Posts: 13549
- Joined: Sun Jul 06, 2008 12:43 am
- Location: 39°06' N 84°30' W
Re: First amp build questions
The Hammond flat-pack transformers mentioned above are great for that purpose.
Re: First amp build questions
Being as there’s people here with sim skills -
Doesn’t C13 0.1uF DC blocking cap feeding the tonestack render the 0.1uF C15 bass cap redundant?
ie change C13 to 0.05uF and link across C15; does that give the same response?
Doesn’t C13 0.1uF DC blocking cap feeding the tonestack render the 0.1uF C15 bass cap redundant?
ie change C13 to 0.05uF and link across C15; does that give the same response?
My band:- http://www.youtube.com/user/RedwingBand
Re: First amp build questions
Hopefully not too late, Mojotone carries a PT that may work nicely. 250v 120mA and 6.3v 1.5A
https://www.mojotone.com/GA-5-Reissue-R ... ransformer
https://www.mojotone.com/GA-5-Reissue-R ... ransformer
Glenn
I solder better than I play.
I solder better than I play.
Re: First amp build questions
I live in Hungary so ordering from Mojotone would be quite expensive, one of the Hammonds mentioned earlier will do the trick. Thanks for the recommendation though!GAStan wrote: ↑Sun Nov 05, 2023 3:01 am Hopefully not too late, Mojotone carries a PT that may work nicely. 250v 120mA and 6.3v 1.5A
https://www.mojotone.com/GA-5-Reissue-R ... ransformer
Re: First amp build questions
I've managed to build the (pre)amp but there is a problem. Besides the nice sounding distorted guitar signal there is a high pitched squeal as well. Here are some things I managed to discover so far:
Gain at minimum: Gain at maximum: Does anybody know what might cause this?
- Knocking on the tubes with a wood stick has no effect
- Noise completely stops when the input is shorted
- The noise has harmonics (probably because of the high gain nature of the amp)
- Gain and mid pots modify the guitar signal as they should but they have some weird effects on the noise
- The noise goes from 2482 hz to 4205 hz as I turn the gain pot from min to max
- With the gain at max the guitar sound is no longer heard, just the squeal
- The mid pot at lower settings reduces the volume of the noise and at higher settings it increases the pitch a bit (but not the volume)
- Volume, high and bass pots work as they should
- Removing first tube has no effect
- Removing second tube reduces the noise slightly
- Connceting the grid of the last gain stage to ground slightly increases the pitch of the noise, connecting the other 3 grids to ground has no effect
- I can hear the squeal from the inside of the chassis very very very faintly, but I can't locate the exact source
Gain at minimum: Gain at maximum: Does anybody know what might cause this?
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Re: First amp build questions
Update: moving the input jack around with its wires changes the pitch of the squeal
Re: First amp build questions
If that's the case, i would improve all the grounds, resolder ground wires, sand connections at jacks and pots, clean with solvent and reassemble. That might kill your oscillation.
Tube junkie that aspires to become a tri-state bidirectional buss driver.