Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: BadCatCubII on June 20, 2022, 12:22:02 pm

Title: Transistor used for tremolo?
Post by: BadCatCubII on June 20, 2022, 12:22:02 pm
Hi everyone,
Long story short, I'm planning to build a single-ended amp with tremolo hoping to use only one triode of a 12ax7 for that effect.

I would like to vary the bias of a pre-amp tube, and I found this thread here: https://el34world.com/Forum/index.php?topic=9255.0 (https://el34world.com/Forum/index.php?topic=9255.0)

I am especially interested in the attached schematic from that thread but can't find the transistor listed, and don't know squat about transistors.

My questions are:
1) Will this work if I attach the port marked "trem" to the cathode of a preamp tube?
2) I can't find the mosfet that is listed in the schematic, will this one work as a subsitute? https://www.digikey.com/en/products/detail/onsemi/SSN1N45BTA/1052982 (https://www.digikey.com/en/products/detail/onsemi/SSN1N45BTA/1052982)

Anything else I need to know?

Thanks in advance,
Ben
Title: Re: Transistor used for tremolo?
Post by: shooter on June 20, 2022, 02:57:28 pm
Transistors - FETs, MOSFETs - Single | Electronic Components Distributor DigiKey (https://www.digikey.com/en/products/filter/transistors-fets-mosfets-single/278?s=N4IgjCBcoGwAwyqAxlAZgQwDYGcCmANCAPZQDaIAzABwCsYclIAukQA4AuUIAyhwE4BLAHYBzEAF8iYAJzUZSEKkiZchEuRBwWUkACYE1RctX4ipSBVpw4AAgBqLdl0ggAqsMEcA8mgCyeBg4AK78eJK6epoAtsQ4aHhczBJAA)


you're looking for a 500V P-Channel mosfet
Title: Re: Transistor used for tremolo?
Post by: sluckey on June 20, 2022, 03:09:09 pm
The LED is backwards.
Title: Re: Transistor used for tremolo?
Post by: BadCatCubII on June 20, 2022, 05:28:54 pm
Thanks, Sluckey and Shooter!

I had noticed that the LED was opposite from the way it is on Merlin's site, so thanks for confirming that, Slucky.

I don't doubt what you say about needing a P-channel, Shooter, but I was able to find a datasheet for the MOSFET in the schematic and it is a 450 volt P-Channel. That is why I suggested the one I did. How do I know what i need?

Do you think this would work: https://www.digikey.com/en/products/detail/microchip-technology/VP0550N3-G/4902412 (https://www.digikey.com/en/products/detail/microchip-technology/VP0550N3-G/4902412)

Thanks again!
Title: Re: Transistor used for tremolo?
Post by: PRR on June 20, 2022, 11:16:48 pm
Quote
you're looking for a 500V P-Channel mosfet

Quote from: BadCatCubII on June 20, 2022, 05:28:54 pm
I don't doubt what you say about needing a P-channel, Shooter, but I was able to find a datasheet for the MOSFET in the schematic and it is a 450 volt P-Channel.

NO!! It is a N channel! On the schematic and on the datasheet!

Title: Re: Transistor used for tremolo?
Post by: shooter on June 21, 2022, 03:31:21 am
 :BangHead:
used the transistor "jingle"
N(ot) pointing IN
P(ointing) IN
Title: Re: Transistor used for tremolo?
Post by: Joel on June 21, 2022, 04:18:05 am
I built this Mosfet tremolo into my Single Channel Reverb about 18 months ago: https://el34world.com/Forum/index.php?topic=26928.msg295792#msg295792  Still happy with it.
Title: Re: Transistor used for tremolo?
Post by: thetragichero on June 21, 2022, 09:04:26 am
Quote from: shooter on June 21, 2022, 03:31:21 am
:BangHead:
used the transistor "jingle"
N(ot) pointing IN
P(ointing) IN
works for bjt

i was scratching my head at all the mention of p-channel fets (i'm sure i have a few, but i have about 500x more n-channel) but hadn't bothered to open up a schematic so just kept my mouth shut
Title: Re: Transistor used for tremolo?
Post by: BadCatCubII on June 21, 2022, 09:36:12 am
This is helpful, thanks! Like I said, I am totally clueless about transistors. :)

Quote from: Joel on June 21, 2022, 04:18:05 am
I built this Mosfet tremolo into my Single Channel Reverb about 18 months ago: https://el34world.com/Forum/index.php?topic=26928.msg295792#msg295792  Still happy with it.

That looks super interesting, Joel, I have some reading to do. :)