Federal AM864 troubleshooting help

[soundguy]

there seems to be a TON of gain in my unit, might be worth looking into to swap the input transformer and use it as a mic pre...

dave

 

[ToobieSnack]

the stock trafo would be good for a ribbon mic right?
what input iron are you considering?
thanks
ts

 

[soundguy]

Im not building a DIY one, its just an off the cuff idea, I havent thought about it at all. Its a line level box so plugging a ribbon mic into it probably wont get you anywhere, but if you could source the appropriate stepup transformer I wouldnt be terribly suprised if the unit was able to provide enough gain to work with a mic. For a line level signal, my input atenuator is on 2...

dave

 

[ToobieSnack]

ok now...dave has his unit working ok with some eceptions as it relates to the meter mis-readings
I am going to start taking some measurements on my unit...
ok remeber I 'm a bit of a newbie so... I have some small questions
initially...

*****UNIT NUMBER TWO********TS

i had started taking measurements and i was getting some odd values.
I discovered that when measureing the filament voltage on the rectifier tube that if I reference one side or the other to ground i was getting the sum of the two 175 volt B+ (like 300+volts)...then after realizing that this could not be right i measured across (series i think ...oops electronics 101 again,,,)
well when i did this i got the 5.x volts that was specified for the tube.

this was apparently a goofy little mistake and I was wondering if i could do this correctly?

I had originally thought I could either clip to the chasis (OR the center tap on the power trafo) and use the other probe to check different nodes...

can someone please advise me as to the correct way to take these measurements?
was this rectifier/B+ reading a rare occurance?
is it only this rectifier that I have to worry about this ? just the filament?
reading filament voltages on the other tubes worked fine with the chassis clip.
can I continue to measure this way?
can anyone offer some "tips"?

as alway your kind comment help and suggestiona are sincerely appreciated
thanks
ts

 

[ToobieSnack]

hello to my friends....
and catch 22 :wink:

i have been ready for this for some time can anyone answer thsi basic question I have... see the reason i ask is that the voltages dave posted ....welll some of them I have much different measurements andI just want to be sure...

thanks
ts

PS MS wwwassssssuuuupppp!!! :shock:

 

[SUPERMAGOO]

with this compresor can i link for stereo operation?? its good idea use for mastering?.
replacement for 6sq7?? :roll: :?
thanks!

 

[ciminosound]

6sq7 replacement possibilities

http://www.mif.pg.gda.pl/homepages/frank/short/054/2/297.pdf

http://www.nj7p.org/Tube1.php?char=Twin%20Diode%20-%20High-Mu%20Triode

You would have to modify the circuit I would guess.

Built with precise components dual mono would be possible, stereo matrix like Fairchild 670 is a different matter entirely.

 

[tk@halmi]

The 6AV6 is an electronically identical part to the 6SQ7, but the packaging is different. While the 6SQ7 is an octal plug part the 6AV6 is a 7-pin compact tube so you would need to change the socket.

Edit: The 6AV6 is a 7-pin tube, not a 9-pin as originally posted.

 

[SUPERMAGOO]

thanks!!! :grin: :grin: :grin:

 

[SUPERMAGOO]

my am864 its working.w/ troubles but work with 6av6!!!! :grin: :grin:

 

[rafafredd]

So, is there any 9pin min subs for the 6sk7???
I´m thinking all 9pin min federal limiter, with 6av6 and 6cG7...

 

[ciminosound]

Raf, the 6BD6 is listed a "similar" to the 6SK7 on data sheets. Haven't done a comparision mysel though.

http://www.mif.pg.gda.pl/homepages/frank/sheets/137/6/6BD6.pdf

:sam:

 

[NewYorkDave]

Rafa, the 6AV6 is 7-pin. So is the 6BD6.

But if you don't have trouble getting the sockets, a 6BD6/6CG7/6AV6 version seems a cool idea to try if you really need to save space. You could even use a miniature rectifier such as 6CA4 or 6X4 if you wanted to keep it completely tube. But don't do it just to save money, since the original tubes used in the Federal are pretty cheap and easy to find as it is.

 

[ciminosound]

Rafa, the 6AV6 is 7-pin. So is the 6BD6.

Oops! Yeah I knew that. Brain Fart.

 

[SUPERMAGOO]

my am864 lives!!!! :grin: :grin:
i used 6ba6 in place of 6sk7 an work fine but compress too much!
and the realese its too long.

in guitar basses sounded very good!

which is the perfect dc hi voltage?

C1 can be change relese time?

R11 can change more or less compresion?? and r7?

R2 its 240 ohms??

current control i dont understand well how to use.to one side pot compress too much to the other side not compress.this control it "ratio"?? :roll:

prodigy people its the best!!! :wink: :thumb:

 

[SUPERMAGOO]

help please!!!

 

[njm]

Been fixing up one of these recently, fully recapped and all resistors checked. New valves, input valves are matched pretty close too. But I'm still getting some odd voltage readings, although the compressor is working.

Main problem is around the V4 rectifier stage. The control voltage coming out of that going to the grids of V1 and V2 is -0.8V, should be -1.4V. And the anode is at 170V, meant to be 140V. I've tried 2 different 6SQ7s there and get the same result from both. R7 is ok and the current control pot is set to 2.5V. I've seen this problem mentioned a couple of times here but didn't see anything about solutions.

The output valve V3 measures a bit funny too, cathodes are at 4.7V and the anodes are 197V when idle (Voltage at the supply output C4 is 205V)

Any ideas people!?

 

[scott2000]

caps came today.

With 47u in place of A and 47u in place of B+C for C4, the limiter wasnt working right.  I removed those, and with the old cap can, everything was working fine, albeit a little noisy.  the voltages I had were 192 for A and 185 for b+c.

I Today installed 22u for A and two 10u for B and C.  Unit is real quiet and works fine however the voltages I have now are 194 for A and 187 or b+c.  I was hoping for 200v.


dave

Did you use (1) 10u for B and (1) 10u for C? I wasn't sure because of the 22u for A..

Thanks!
Scott

 

[gyraf]

This was 10 years (!!) ago. SoundGuy was last active here about a year ago...

Jakob E.

 

[emrr]

Too bad all the other threads didn't continue here, we'd be at hundreds of pages.