Princeton 5F2A / 6G10

[stingray_65]

WOW!
I never knew a single ended amp could sound so good or be so LOUD!

I JUST finished a 5F2A

putting it in a BF style combo with an 8" weber blue dog

Holy Smokes this thing ROCKS!

My voltages are a little high in most places (see attachment)

Using a MM FTPP Tone Clone PT

RCA 5Y3GT from my tube pile
RCA 12AX7 black plate date 5724
RCA 6V6GT NOS dated 5832

the OT is a cheap Speco line matching xformer and may get replaced later, but it has a 8&4ohm out and what I calculated to be 4k ohm primary.

I've been rolling tubes all morning in it, the RCA 12ax7 is hands down the most tasty preamp tube I have with an old Zenith being a close second.

for the power tube I've had every thing I could find in there from a russian 6n6C and a real sweet sounding RCA 6K6GT

I really didn't care for the japaneese gold pin realistic 6v6's and my ancient KenRad gave up the ghost when I hot swapped it in

and WOW for a SE amp the only hum I can hear with nothing plugged in is less than a wisper and even then I have to have my ear next to the speaker cone

I'm not so concerned with my higher HT voltages, but I am a bit concerned with the heater supply running at 7.0 VAC. the jewel pilot light looks like a red beacon! I can only imagine the stress on the heaters.

the yellow recto heater wires have 5.4 V under load

my other concern is the OT primary, is 4K too low? I see 5K suggested many places

[tubeswell]

Originally Posted by stingray_65

WOW!
I never knew a single ended amp could sound so good or be so LOUD!

I JUST finished a 5F2A

putting it in a BF style combo with an 8" weber blue dog

Holy Smokes this thing ROCKS!

Glad it worked out. Those simple amps are not to be underrated.

Originally Posted by stingray_65

I'm not so concerned with my higher HT voltages, but I am a bit concerned with the heater supply running at 7.0 VAC. the jewel pilot light looks like a red beacon! I can only imagine the stress on the heaters.

the yellow recto heater wires have 5.4 V under load

You can get the voltages down a 1/2V or so with back-to-back diodes on each side of the relevant PT secondary winding. Use 6A diodes on eth heater and 3A diodes on the recto

Originally Posted by stingray_65

my other concern is the OT primary, is 4K too low? I see 5K suggested many places

you can plug twice the rated secondary speaker load in to get the reflected load to 8k. i.e. if the secondary tap is rated for 8R, plug 16R worth of speaker(s) in. (Warning - this should give you even more power)

[stingray_65]

Tubeswell to my rescue again

just so we're on the same page about back to back diodes, do you mean like this? (see attachment)

[tubeswell]

See attachment. Should get about .7V drop. You need 3A-6A diodes (rated at say 20V min) on the rectifier windings, because of the higher current draw.

But in that little amp you should get away with 1A diodes (1N4007) on each side of the heater winding if you are using a 6V6 and a 12AX7, because the heater draw will be 750mA. (But if you use a 6L6 and a 12AX7, you will need 2A diodes, or more, on the heater winding)

[stingray_65]

Well I did as you suggested Tubeswell

In the process I found a cold solder joint (I'm assuming) on the recto socket where the 5V heater and B+ meet

when I put the diodes on the 5V and 6.3V lines it dropped the voltage way low and the whole thing sounded like... well it wasn'y pretty

Funny thing tho my 5v heaters were now reading 5.3v before the diodes.

I took the diodes out of the circuit and reconnected the leads from the transformer directly to the socket again and was still maintaining 5.3v so I'm assuming I had a cold joint there and the recto want drawing enough current giving me an arificialy high reading when I checked it at first.

now with the diodes back to back on the 6.3v heaters I was getting only 5.5V

it took the tubes a long time to heat up and it was a bit muddy.

so I removed one set of diodes and the voltage is 6.58v under load and the sound is PERFECT.

I was concerned that both legs weren't balanced and it would hum or give me some other issues, but I believe its even quieter now!

the light seems the right intensity and everything

I really would like to thank you again for getting me on the right path here

RAY

[tubeswell]

Well now you have fixed it I can say that with suggesting having the diodes on both windings, it was a bit of a stab in the dark on my part as to how much it would drop the voltage. And anyhow you experimented and found out how to make it work - so you should take the bow.

[PremiumPlus]

Yeah, I'm lucky enough to own an original 1960 5F2A Princeton Tweed, and I'll testify that they sound terrific! I've got a little Jensen MOD 8" speaker in mine right now and funny but it smokes both my Weber 8"ers. I've got the expensive Alnico one and the $35 dollar too, but the little MOD kicks serious butt.
I have gigged mine regularly with the church praise band and it keeps up pretty well. An amazing amp.

[stingray_65]

I was showing the amp off to a serious guitar player just yesterday.
he COULD NOT put it down.
luckily he's a 2nd shifter and needed to go to work and left after 2 hours.

he'll be over friday morning to start piecing together one

I'll seriously considder the jensen on his build just so I can hear one.

as it turned out the little ceramic Fender speaker that came with the baffle board wasn't bad at all.

After reading a few posts about basic trouble shooting, I had heard mentioned retensioning tube sockets, a quick wiggle of the 6V6 and I had it open and a small pick in there tightening the sockets. WHAT A DIFFERENCE

Ray

[PremiumPlus]

Yeah, for about $20 you can't go wrong with that little MOD Jensen.