Hi folks,
I wonder if anyone can put my mind at rest, or guide me a little please? I built a
@Modulus_Amps 5f2a kit last year and have been thoroughly enjoying it since. But I felt I should try and understand the workings of the amp a little better rather than just following the excellent layout provided by Modulus. Anyway I finally got round to checking some voltages tonight and they seem a little low from what I've read online on various forums. I have:
12AX7:
1 - 159V
2 - 0V
3 - 1.1V
4 - 3.2V AC
5 - 3.2V AC
6 - 153V
7 - 0V
8 - 1.2V
9 - 3.2V AC
6V6:
1 - 0V
2 - 3.2V AC
3 - 306V
4 - 268V
5 - 0V
6 - 0V
7 - 3.2V AC
8 - 16V
Power Transformer - 279V AC
Filter caps: 316V, 316V, 269V, 234V
Heater wires: 6.49V AC
I'm not sure what would cause them to be low, perhaps the power transformer, but what is the long term effect? Should I be worried, look to mod something or leave it as it is?
Much appreciate any help.
Cheers,
Graham
Comments
I'd say plug in and play and let your ears decide.
I assume the Rk is 470r? If so, you're biased around 82% (a+g2) which isn't stressing the 6V6 at all. Will probably last forever if you leave it as is.
Rift Amplification
Brackley, Northamptonshire
www.riftamps.co.uk
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
I could tell the difference between a modern and an old-production GZ34 when I had a friend swap them in an amp was playing through, without telling me which it was.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
Is there any known trustworthy source for NOS ones? And which NOS ones are considered to be good? (all of them? )
Good job I didn't also buy a second JJ 5Y3 at the same time to have a spare...
What valves do you currently have in there?
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
Is this the right one? It seems to be 5Y3WGTA, and I had a quick look online at some of the valve information sites and I'm not convinced it's the same as a standard 5Y3... EDIT: Actually I just now had a quick look at Watford Valves and they seem to be recommending it for guitar amps, so maybe it is ok.
https://www.ebay.co.uk/itm/296341535725?itmmeta=01HVFDC52S2M78J2425AH0JAY4&hash=item44ff54fbed:g:y7kAAOSwI~JmDnB~&itmprp=enc:AQAJAAAA0DnQsjPyT0dJWc9QsV3hhskfFF3fWCdYHzgOQP/5v5Ty7cRhohqKbOmf0KA0hgCNhQOgIJmLoJxb0yJoYWQndgZHMshkDDHI4zYFTSvVshfAY76ISxJK/8xwZHtf+1+CpLZ8punP8F7omsI0vzbzhKXDTTN5BYDY3OQbRKjoh/F2db2435/4HsKNX7Tg3OxtE1WqwUsztWyO63bgn1ja4wiG+teHco494mklq0eEo89KsZMzcmTM2iKJgc38FlcjnAiaWZRSXtE1c9YOI3eX4qQ=|tkp:Bk9SR8TRsO3bYw
Rob's site is awesome. What type of power reduction is it, is it like power scaling or VVR? If so that's definitely going to make more difference than changing valves, speakers etc. which at best is usually just tinkering round the edges...
https://photos.app.goo.gl/iN8o8uLNDvY6fTBt7
Remember that’s there’s an impedance difference - if the amp is properly optimised for a 6V6, using a 6L6 will actually *reduce* the power, and probably give a more middy tone (since it’s then a high mismatch). So I expect that amp has been purposely designed to take both types, or even optimised for the 6L6, which will then give more power and a wider frequency response.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
This its the transformer you have installed in your amp, the voltages look spot on.
https://modulusamplification.com/champ-5f1--princeton-5f2a-style-power-transformer-240v-3392-p.asp
The voltages internally are affected by the wall voltage a lot, up here I can measure anything between 230v and 248v at different times on the same day and you can hear the difference in the amps as a result.
You could fit a transformer to get higher voltages, higher voltages will get you a little more power and may sound a tad bit brighter. But even at these wattages still too much power for most homes.
Since you are exploring rectifier options, You could also fit two 1n4007 diodes on a switch to bypass the valve rectifier, you will hear the higher voltage difference.