5F1 Rectifier

[fabiomayo]

Hello, everyone.

I'm not even sure since I've been lurking around ever since
the move but I believe this is my first post. Hello!

I finally got (almost) all the parts to my first amp build. It's
a 5F1 tweed Champ with a Princeton Tone control (defeatable).

One of the parts missing is the 5Y3 rectifier. I'd rather not spend
on more tubes right now. Could I use the 5U4 (JJ and some kind
of NOS, Sylvania perhaps) I have? I also have a JJ GZ34...

Thanks a lot!

[steve]

Hello, everyone.

One of the parts missing is the 5Y3 rectifier. I'd rather not spend
on more tubes right now. Could I use the 5U4 (JJ and some kind
of NOS, Sylvania perhaps) I have? I also have a JJ GZ34...

Thanks a lot!

The 5Y3 draws 2A of filament current from the 5v winding on your power transformer. The 5U4 draws 3A of filament current. If the 5V winding is rated for 3A you can use the 5U4. The GZ34 is rated for 2A, but has lower votage drop compared to the 5Y3 and 5U4.

What power transformer are you using? If your secondary voltages are low enough, you don't need to use a tube rectifier at all, SS diodes will do. The only advantages of a tube rectifier are that it knocks the B+ down a bit and some rectifiers (but not all) have slow start up characteristics so that you don't need a standby switch.

steve

[fabiomayo]

Thank you so much for your answer.

I'm using Mercury FTCP-59. I'll shoot Paul an email to find out if
it's good for 3A. The voltage drop would be the same with a 5Y3
and 5U4? In any case I could always adjust the resistor string to
get the correct voltages, right?

Thank you very much!

[fabiomayo]

BTW, this tranny is spec'd as 325-0-325 secondary...

[TD_Madden]

think both 5Y3 and 5U4 have 50v drops.

[steve]

think both 5Y3 and 5U4 have 50v drops.

True, but the voltage drop for a 5Y3 is 50v @ 125mA, for 5U4 it is 50v @ 275mA.

steve

[TD_Madden]

yep.

[MWJB]

If your tranny really delivers 325VAC at the secondary you should be OK with a GZ34, which is also a 2A rectifier. You may as well wait until you get the thing together and see what your voltages (loaded with tubes) actually are.

In reality you may only see a 20-25v drop in B+ between vintage 5Y3 and solid state rectifiers in a Champ.

By playing with resistors in the power supply, you can only vary screen & preamp voltages, which won't help if your plate voltage/dissipation are too high (though this is unlikely with a 325VAC B+ secondary).

[fabiomayo]

Thank you all very much for your responses...

I got a response from Paul saying this PT can handle the extra current.
I guess you're right about me not being able to reduce plate voltage.

In any case, I suppose the best approach is to hook everything up and
check the voltages.

Thanks for all your thoughts.

BTW I have a VERY newbie question:
How do I measure said voltages? Do I just ground one of the multimeter
connections and connect the other to B+1, B+2, pin 3 V1, etc...?
Is that right?

Thanks!

[MWJB]

Yes, ground the common (black) probe to the chassis and clip it in place then, with one hand only, use the red probe to record your voltages. In fact, I would very strongly suggest that you invest in some meter leads with crocodile cllips & wire grabbers. Then you can connect up with the amp unplugged, measure a specific voltage then power down & unplug. Repeat for the next voltage measurement.

This way may seem a bit laborious, but until you are totally familiar with what you're doing, it will be much safer.

It's also often easier/safer to measure voltages at the component on the board (cathode resistor, plate resistor) rather than at preamp tube pins.

If you have wired your heaters as a twisted pair, you will need one meter probe on one leg of the heaters (power tube pin 2) and the other on the other leg (power tube pin 7 on a 5F1), when checking heater voltage.

[Bruce / Mission Amps]

Right. I wouldn't be surprised to see this PT run B+ at around 410vdc to 435vdc with a 5U4.
Much too high for a good sounding SE Class A 6V6 in my opinion.
Stick with a real NOS 5Y3GT.

[fabiomayo]

*Sorry for the loooooong post*

I would really like to thank everyone that chimed in here and in the layout
thread I started. You've been very VERY helpful indeed. And it's sincerely
appreciated.

I finished soldering last night, slept on it, re-checked everything this morning
and fired it up with great success. Here's a few pictures. It doesn't have
a proper enclosure yet. Voltages in the end for those interested...













Tell me what you think. It sounded real fine from the startup. I used a
12AX7 JJ, a ANOS Sylvania 6V6 and a NOS 5U4 (don't know which brand).
There is an intermitent noise issue on mid-to-high settings and I found a
bad solder joint at one of the input jacks. To be redone yet. Sadly I killed
two 12AX7 while searching for this .

All in all it's pretty quiet and sounds great. Sounds clean(ish) until halfway
up with my P90 neck + single coil bridge tele and really high gain after 2 or 3
o'clock. the tone control is defeatable and I like it better out of the circuit.
Taking it out gives a small boost but not much. I found the tone control to
be useful in adding brightness to the overall sound but personally I didn't like
it. Perhaps it's the ceramic cap I have in there... So far I'm not considering it
to be useful enough. Plus the single volume control is way cool in my book

I also tried very briefly the GZ34 JJ and got a little brighter tone. Didn't care
for it too much. Using a 6V6 JJ I got better string separation and a little
(and I mean very little) more highs. The bottom is punchier and juicier with
the 6V6 JJ. My preferred tone. But then again the difference is subtle to my
ears.

I played it through the speakers on my Dumble clone combo: a Cannabis Rex
and a Private Jack wired for the correct 4 ohms impedance. I briefly played it
through the Weber on my Tremolux clone and it sounded better. Since it's 8
ohms I preferred not to take any chances. What do you guys think? Can I run
the 5F1 through the 8 ohms speaker? Opinions seems to indicate that it's safe
but I just don't feel right...

[fabiomayo]

Anyway... Thanks everyone for your opinions and great advice. Here are the
voltages. My preamp tube plate is closer to 200V and I thought in these amp
it should be around 150V. I think the 6V6 are okay... What do you guys think?

Preamp: 12AX7 JJ; Power: 6V6 Sylvania; Rectifier: 5U4 (unknown NOS)
12AX7
pin 1: 198.1
pin 2: 0
pin 3: 1.57
pin 6: 199.3
pin 7: 0
pin 8: 1.45
6V6
pin 3: 1.74
pin 4: 359.2
pin 5: ~10mV
pin 8: 18.00
Filament: 7.26

Preamp: 12AX7 JJ; Power: 6V6 Sylvania; Rectifier: GZ34 JJ
12AX7
pin 1: 213.5
pin 2: 0
pin 3: 1.67
pin 6: 206.5
pin 7: 0
pin 8: 1.64
6V6
pin 3: 1.93
pin 4: 378.2
pin 5: ~5mV
pin 8: 19.70


Preamp: 12AX7 JJ; Power: 6V6 JJ; Rectifier: 5U4 (unknown NOS)
6V6
pin 3: 1.87
pin 4: 335.8
pin 5: ~20mV
pin 8: 19.83