scroungin treasure

[Phil_S]

Hi Mark. I am a bit of a junk collector and this was a wild hair junkbox build. I acquired that PT on the cheap from eBay. I don't remember if it was included on a chassis or if I just lost my mind and bid for some random PT. In either case, I am reasonably sure it was well below my $20 (w/ S&H) price point for mystery iron. I offer this so you understand the choice of PT was driven by lunacy, not by logic. IOW, I started with the PT and tried to find something that would work with it.

As I recall, I employed a modest value high wattage resistor between the B+ supply and the plates to drop just a few volts to get plate voltage down to 450, VaMax according to the spec sheet. I see R13 = 1K and that could well be the final build, but I don't remember. I am not sure how to do a proper in-situ measurement of power out, but all the readings I got suggested to me that I must be getting around 2.5W per triode or 10W total. This amp is not very loud, but I attributed that to the concertina and generally the limited amount of gain from just one dual triode preamp with a tone stack between them. Unfortunately, I don't seem to have recorded a set of voltage measurements. Maybe, if I have time and can screw up my courage, I'll publish an updated schematic. The high voltage in this amp gives me the willies.

Back to the question, do we need 920VCT? I think not. I don't have the experience to really know. I am comfortable suggesting it is a good PA design for the many 400-0-400 PT's with anemic current specs that are floating around. There's no good reason to push the tubes to the limit. I only did it because I had the PT and because I could.

[Firestorm]

920V CT would be cool with an EL34 and economy power supply to run the screens at half B+. We don't seem to take advantage of the 34's high plate rating because we're always running the screens just a few volts below.

[M Fowler]

Thanks Phil.

Perhaps a regulated PS for the screens and 920vct for the EL34 plates.

[Phil_S]

I took a minute to look at the amp, outside only. I had the <wisdom> to write on the OT, which says it came from an Arkay FL-10, and by the voltage method I determined it is 9K:4-8-16. The PT has surface rust. I can't imagine it came from the same amp, as the FL-10 was probably PP 6V6. (I have iron from the FL-30 in a JTM 45 build and it ran PP EL34; just a coincidence that I stumbled across two of the same brand on eBait for cheap.) I don't know where the PT came from. Judging by it's physical size, I will guess it is in the 100-150mA range. It is too puny, IMO, to support a couple of big bottle tubes...maybe a pair of 6L6. I don't have recorded test results. When I test an unknown PT, I usually load it to establish it can be used for the intended purpose and not for its limit. As you know, the only real way to determine the limit is to let the smoke out and what good is that? Since the target tubes were 6SN7, I probably didn't bother to test it.

[eniam rognab]

what up

i also got some some smaller non tube transformers that might make a sweet solid state amp (i might stick one bizarre looking tube and just light the heater up and tell people thats where the tone comes from)

the lil OT is labeled 2k on one side and 8 ohm on the other, three leads per side. 12KF200 on top

why three leads on the 8 ohm side? White-Black-White

the DCR is ~2.9-3.3 ohms all around w-w, w-b, b-w couldnt really tell a difference other than color and placement.

the 8 ohm marking leads me to believe this is an output transformer but ive been wrong before and ill be wrong again.

while were on the subject my UOTs are labeled P(blue) and B(red). this is plate and b+ right? then i run wire from the ST terminal and the matching ohm terminal to the voice coil? or is it the other way round?

thanks peeps!

[eniam rognab]

these were in a box of carbon comp resistors, in a bag marked bad, the resistance test would have shown open

ten NOS bumblebees .022! schwing!

[menger66]

Those bumblebees look NOS 5 pairs the buyers in japan would pay 500$ for those, you lucky dog, I sold 13 caps on ebay soldered to a board for 400$ one time, excellent score mark

[eniam rognab]

Those bumblebees look NOS 5 pairs the buyers in japan would pay 500$ for those, you lucky dog, I sold 13 caps on ebay soldered to a board for 400$ one time, excellent score mark

dayum! whats the phone number for japan?

these are rated @200 Vdc right? other than selling them, what would be the "best" application for these?

my vintage les paul?

[menger66]

They have a black 4th band there 400v, they were stock tone caps in les pauls in the 50s, best app is sell and buy amp building supplys, they should be red red orange black, there way to valuable to use in a build though some old amps have them in them i just found a bunch in a TV chassis but only 1 .022, just list them on ebay they will sell i beleave NOS go for 129$ a pair i've sold tons of used pull sets for 69$ mark

[eniam rognab]

They have a black 4th band there 400v, they were stock tone caps in les pauls in the 50s, best app is sell and buy amp building supplys, they should be red red orange black, there way to valuable to use in a build though some old amps have them in them i just found a bunch in a TV chassis but only 1 .022, just list them on ebay they will sell i beleave NOS go for 129$ a pair i've sold tons of used pull sets for 69$ mark

i have a sweet, dirty fuzz pedal that would take like five of em... im sorry ill stop screwin around

thanks for the info... these might end up over in the for sale section here maybe 8 of em retirement ya know

im really not cool enough for these!

[Firestorm]

That find is just too sweet. In a few years, we'll be calling it apocryphal.

[dorrisant]

Please don't waste them in a pedal.... I'll trade you two of them for a sweet germanium fuzz! Like a Buzzaround... ?

Tony