New 5F1 build: some voltages

[Jonny toetags]

I just completed my 5F1 build and have been testing it and burning it in.
I just wanted to share some voltages with you guys.
It's my first 5F1 build so I just want to make sure things look normal.
I used Classictone's PT and OT and used this layout:
http://site.triodestore.com/5F1layout40-18019.pdf

Here are some readings:

[eschertron]

The voltage on pin 8 of the 6V6 (cathode) will be a good one to record also.

edit: are you sure that you're dropping 50vdc across the OT primary winding? seems excessive! I'd expect pin 3 of the 6V6 to be higher than 336vdc. That might look right to someone else, though

[Jazz P Bass]

There are a few 'key' voltages that where omitted.

V1: Pin 3 Pin 8
V2: Pin 8

[Jonny toetags]

6V6:
20v pin8
361v pin3

12ax7:
1.57v pin8

heaters: 3.35v
1,56v pin3

[Jazz P Bass]

Looking good.

How does it sound?

[Jonny toetags]

Looking good.

How does it sound?

Amazing actually.
I just received my speaker today and brought it to the rehearsal place just to see what it sounded like cranked. Simply amazing.
Sounds like Neil Young.

[Chuck H]

Sounds like Neil Young.

Love that guys tones! Which is a good thing. If it weren't for good tone I don't know if I could hang listening to his lead guitar work

[Jonny toetags]

Love that guys tones! Which is a good thing. If it weren't for good tone I don't know if I could hang listening to his lead guitar work

lol

[g1]

Love that guys tones! Which is a good thing. If it weren't for good tone I don't know if I could hang listening to his lead guitar work

lol

Don't get me started. You guys should be made to hear ARC in a glorious loop for days on end.

[Jonny toetags]

The only thing I am noticing is that this amp has a very low hum to it, even with the vol at min (just switched on).
It's not super loud, but when you leave the amp on and turn it off...you can notice it.

[loudthud]

If you get hum immediately when you turn the power on before the tubes warm up, it is the magnetic field from the power transformer coupling to the output transformer. Try to rotate the output transformer to a position where there is no hum pickup.

[eschertron]

The only thing I am noticing is that this amp has a very low hum to it, even with the vol at min (just switched on).
It's not super loud, but when you leave the amp on and turn it off...you can notice it.

Correct me if I'm wrong, but I'm guessing from the layout that the heaters have one leg grounded at the PL just like Leo did. It'll give you less 60Hz hum if you take two 100R resistors and make an artificial center tap for the filament supply.

Also, any SE amp will have less ripple rejection than a PP amp, the only fix for that is to add more filtering. Back in the day, can caps were expensive, so Leo (again, as any self-respecting entrepreneur would do) used the least amount of filtering he thought he could get away with. Personally, I'd put the biggest res cap in there that the rectifier tube allows, and move the 16u cap over to the screens. That will reduce any hum that sounds like a 'buzzy' 60Hz.

Those are the two primary sources of 60Hz-and-harmonics noise in that amp. Which one predominates depends on how bad the heater hum really is.

[DrGonz78]

It'll give you less 60Hz hum if you take two 100R resistors and make an artificial center tap for the filament supply.

Sorry to interject a question here, but I must. I was wondering about a 5F1 that has a center tap on the heater supply and if you can still add those resistors or if it just makes a ground loop? I actually built mine with a center tapped heater supply and the two 100R resistors. It does not hum bad at all and sounds great.

Also, the crew here told me if you have a center tap for the heater windings that it could be connected to the cathode of the output tube too. I only grounded my center tap and then not really knowing better put the two 100R resistors to ground from the pilot light. I would snip off the resistors if I thought it was causing a problem.

[eschertron]

A filament CT is a bonus and should be used! That is, unless you're going to make a humdinger circuit; but that's really for the builder who wants to exorcise the last fraction of a decibel (centibel? millibel?) of heater hum.

I'm told one or the other works fine (CT or the resistors), no need to use both. Certainly not recommended would be to reference one of them to ground and the other to some different potential, like the output tube's cathode.

Merlin's preamp book gives some theoretical and practical insight to heater referencing (and he seems to be a proponent of the humdinger). Raising the heater reference to the cathode, about 20 - 23vdc (?) in a 5F1, may make a difference. I haven't tried it yet. Will do when I get around to that last centibel of hum, though!

[DrGonz78]

Sorry again to interrupt the flow of the OP's questions, but I thought it might be somewhat of interest to him too. I think I will snip out those resistors after all since I really did not realize they weren't necessary(redundant) when I built the thing last year. I understand that the center tap would float above ground when connected to the cathode and I too have yet to try that myself. Also, have thought of picking up Merlins book and will have too soon. Right now just dissecting a great Craig Anderton book at the moment. Thanks for the response and again I hope it relates well to the original post content.