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Princeton kit build
Posted: Sun 05/22/22 1:20 pm
by yello
A friend sent me a Mojotone 5f2a Tweed Princeton kit a while back, and I think that'll be my next amp build.
This is the schematic and layout:
https://www.mojotone.com/Amp_Kits/Tweed ... 2A_SCH.pdf
https://www.mojotone.com/Amp_Kits/Tweed ... F2A_WD.pdf
Here are my introductory questions:
1) Does anyone have some fun mods they like on a 5f2a? Modify or remove the NFB? Lower the 12ax7 cathode cap? Different value for the 6V6 cathode cap?
2) I'm using a small chassis I have on hand, and using a cap can would save me some space. I happen to have a 20/20/10/10 uf cap can on hand, which should work fine for the 16/16/8/8 uf in the schematic. My question is, the cap can shares a ground for all caps, but that makes a common ground point for caps in different amp stages - is that a problem, and what would the problem be?
Re: Princeton kit build
Posted: Sun 05/22/22 1:38 pm
by Bieworm
yello wrote: ↑Sun 05/22/22 1:20 pm
A friend sent me a Mojotone 5f2a Tweed Princeton kit a while back, and I think that'll be my next amp build.
This is the schematic and layout:
https://www.mojotone.com/Amp_Kits/Tweed ... 2A_SCH.pdf
https://www.mojotone.com/Amp_Kits/Tweed ... F2A_WD.pdf
Here are my introductory questions:
1) Does anyone have some fun mods they like on a 5f2a? Modify or remove the NFB? Lower the 12ax7 cathode cap? Different value for the 6V6 cathode cap?
2) I'm using a small chassis I have on hand, and using a cap can would save me some space. I happen to have a 20/20/10/10 uf cap can on hand, which should work fine for the 16/16/8/8 uf in the schematic. My question is, the cap can shares a ground for all caps, but that makes a common ground point for caps in different amp stages - is that a problem, and what would the problem be?
1. Build it stock first, do the mods later.. you might wanna anticipate on possible modding, building those areas with additional turrets
2. I think you know that you've already answered your own questions. If not, read the docs on grounding schemes again
Re: Princeton kit build
Posted: Sun 05/22/22 4:00 pm
by yello
Bieworm wrote: ↑Sun 05/22/22 1:38 pm
1. Build it stock first, do the mods later.. you might wanna anticipate on possible modding, building those areas with additional turrets
2. I think you know that you've already answered your own questions. If not, read the docs on grounding schemes again
On #2, yeah my instinct is that it is bad, but why? I assume because it is a potential noise/hum issue?
Related question on the cap can - can I just use 3 of the 4 cap terminals in the cap can and leave one unused? Then use a separate same value cap for the preamp section? I don't know if it is standard or advisable to not use all sections of a multi-section cap can (or why/why not).
Re: Princeton kit build
Posted: Sun 05/22/22 10:30 pm
by Bieworm
You can use half the can cap without issues.
If you tie preamp and power amp grounds together you will likely get hum. In fact, it's a safe bet for getting hum for sure.
You will harvest the most success when you put the filter cap for a stage as close as possible to that stage's circuit.
Re: Princeton kit build
Posted: Wed 06/22/22 3:12 pm
by yello
Re: Princeton kit build
Posted: Wed 06/22/22 7:58 pm
by Unit_1
Hey and you can put an LED behind that lens and use it as the indicator light!!! Awesome!
Re: Princeton kit build
Posted: Wed 06/22/22 11:22 pm
by yello
Unit_1 wrote: ↑Wed 06/22/22 7:58 pm
Hey and you can put an LED behind that lens and use it as the indicator light!!! Awesome!
Yep, that’s the plan!
Re: Princeton kit build
Posted: Thu 06/23/22 10:19 am
by yello
Unit_1 wrote: ↑Wed 06/22/22 7:58 pm
Hey and you can put an LED behind that lens and use it as the indicator light!!! Awesome!
Here is a photo from another similar amp I've been slowly working on, showing how I implemented the pilot light behind the lens:
