5f2a voltages

gdculley

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 

goldtop

A little low, but I guess there's a 5Y3 fitted and they are famous for gobbling B+.

I'd say plug in and play and let your ears decide.

gdculley

Thanks @goldtop - yes there's a 5y3 fitted. It does sound very nice, so I'm happy with it, just wanted to check it's as it should be! :-)

RiftAmps

Those numbers seem fine to me, I certainly wouldn't be worried. Install a 5V4 if you want to bump them up a little.

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.

ICBM

Doesn’t look like a supply voltage or PT problem to me - the heater voltages are bang on. Most likely a bit too much drop in the 5Y3 - modern (especially Russian) ones are rubbish, if it has one I would recommend getting an old-production USA-made one, they’re not expensive and will last forever in that circuit.

gdculley

Thank you all for your help, fantastic advice as always! I'm pretty sure I have a JJ 5Y3 in there at the moment so I will try and get hold of an old USA one and see if that's changes much. If not I'll leave it as is. I've learnt a little more about how it works anyway, so maybe I'll push myself and try another build. :-)

Dave_Mc

gdculley said:

Thank you all for your help, fantastic advice as always! I'm pretty sure I have a JJ 5Y3 in there at the moment so I will try and get hold of an old USA one and see if that's changes much. If not I'll leave it as is. I've learnt a little more about how it works anyway, so maybe I'll push myself and try another build. :-)

I can't help you with the voltages, but if you do try a NOS rectifier I'd be interested to see how it sounds compared to the JJ. I've got a 5F2-A clone too which currently which has a JJ 5Y3 in it too- I initially had all new-production valves in it (Tung-Sol IIRC, which are pretty good) but then I found a NOS (actually more like used!) Brimar 6V6 (amazing) and Sylvania 12AX7 (very good, but I'm not sure it's really any better than the Tung-Sol, really, I just left it in there because "Why not?") in my uncle's radio valve stash, which I've been using ever since. He didn't have any old 5Y3s unfortunately...

gdculley

Interesting Dave. I'll post back once I get round to trying a different 5y3. Although I think I'm right in saying the 5y3 might alter my voltages but probably won't have much effect on the tone of the amp. Your comments have me thinking I should maybe try a few valve swaps just for fun though!

ICBM

It is really surprising how much the rectifier affects the sound, even though it’s not in the direct audio path.

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.

gdculley

Ah that's interesting! I'll definitely have a play around in that case!

Dave_Mc

ICBM said:

It is really surprising how much the rectifier affects the sound, even though it’s not in the direct audio path.

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.

Interesting, thanks And GZ34s don't sag as much as 5Y3s, isn't that right? (Whether that means they affect the tone more or less is another thing, though!)

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...   

Dave_Mc

gdculley said:

Interesting Dave. I'll post back once I get round to trying a different 5y3. Although I think I'm right in saying the 5y3 might alter my voltages but probably won't have much effect on the tone of the amp. Your comments have me thinking I should maybe try a few valve swaps just for fun though!

I've never swapped the rectifier so listen to @ICBM on that front, but I did swap in several preamp and poweramp tubes- my 5F2-A is by Robin Wood, and it's incredibly easy to get at the valves. I.e. you don't even have to remove a back panel, you can just swap them without having to remove anything other than the valve. Actually nearly too easily, you have to sit and wait for them to cool!

What valves do you currently have in there?

ICBM

Dave_Mc said:

Is there any known trustworthy source for NOS ones? And which NOS ones are considered to be good? (all of them?  )

Any, but the JAN Philips/Sylvania is probably the best, one of the most common and one of the least expensive since it was made in large quantities up to the end of valve production in the West. Typically around £20, which is a bargain.

gdculley

Dave_Mc said:

What valves do you currently have in there?

Hi Dave. I started out with all JJs in the amp but was struggling to get much breakup at home volumes. So I swapped the 6V6 for a Tungsol and that helped a little. But then I added the Rob Robinette power reduction mod, initially in an external box to see if I liked it, and then later added to the chassis. With that and the Tungsol I get some nice champy style breakup at just about home levels!

Dave_Mc

ICBM said:

Dave_Mc said:

Is there any known trustworthy source for NOS ones? And which NOS ones are considered to be good? (all of them?  )

Any, but the JAN Philips/Sylvania is probably the best, one of the most common and one of the least expensive since it was made in large quantities up to the end of valve production in the West. Typically around £20, which is a bargain.

Thanks

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

Dave_Mc

gdculley said:

Dave_Mc said:

What valves do you currently have in there?

Hi Dave. I started out with all JJs in the amp but was struggling to get much breakup at home volumes. So I swapped the 6V6 for a Tungsol and that helped a little. But then I added the Rob Robinette power reduction mod, initially in an external box to see if I liked it, and then later added to the chassis. With that and the Tungsol I get some nice champy style breakup at just about home levels!

Yeah from what I remember a JJ 6V6 is probably slightly louder than a Tung-Sol- a lot of people say the JJ is almost halfway to a 6L6 in terms of tone and volume. I'm not sure I'd completely agree with that (I did try a 6L6 in my VHT Special 6 and it was a lot louder and bigger-sounding than the JJ 6V6!) but at the same time I sort of know what they mean, it does have a little bit more of that "bigger tube" flavour. To my ears the JJ 6V6 works better if you're after a more Black Panel type of tone (it's brighter, crunchier and maybe a bit more scooped), the Tung-Sol is better for tweed I think (it's warmer, creamier and bassier). (But funnily enough I would say the JJ 12AX7 is a bit dark/warm for Black Panel, or even tweed tones... I'm not really that keen on it.)

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...

springhead

Dave_Mc said:

ICBM said:

Dave_Mc said:

Is there any known trustworthy source for NOS ones? And which NOS ones are considered to be good? (all of them?  )

Any, but the JAN Philips/Sylvania is probably the best, one of the most common and one of the least expensive since it was made in large quantities up to the end of valve production in the West. Typically around £20, which is a bargain.

Thanks

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

Yes that’ll do the job. I have one of those in my 5E3/Deluxe. 

gdculley

Dave_Mc said:

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...

I installed his 10% power switch mod, which is a tweak on his 1/4 power mod mentioned just before it on his site. If you read through that section of his website he talks about people often preferring the more sever power cut due to the way we perceive volume. So I tried it in an external box, slightly sceptical it would sound good, and I was really impressed with how little it affected the tone of the amp, at least to my ears anyway! 

gdculley

Here's a couple of photos of it installed in my amp...

https://photos.app.goo.gl/iN8o8uLNDvY6fTBt7

ICBM

Dave_Mc said:

Is this the right one? It seems to be 5Y3WGTA

https://www.ebay.co.uk/itm/296341535725

Yes.

Dave_Mc said:

I did try a 6L6 in my VHT Special 6 and it was a lot louder and bigger-sounding than the JJ 6V6!

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.

Modulus_Amps

@gdculley ;
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.