Need some help troubleshooting an Ashdown FA-60

[milkbone]

Hi all!! I'd love to get some input and ideas on which direction to go.

I have an Ashdown Fallen Angel 60 which is the first version (no DSP). I have already had to replace the PT (which was succesfull).

Now the problem is, while playing a while back the volume cut down to about half. I tried different power tubes (EL-34s) and it was the same. I've swapped out the Pre's and the PI with known good 12AX7s,, same.

I know from reading and research that these have been plagued with bad transformers which is how I was led to this site. I suspected the OT mabey going south. I don't know how to check the OT except to use a multi and check the resistance from the center to the outside taps on the primary. I'm getting 138 on one side and 128 on the other. According to some research, this is acceptable (5-10% common).

There is no brown or burnt components that I can see. There are two resistors that are not "cylindrical" (don't know if they were to begin with) they read " W22 1KO 5%" and are in the power section. I have downloaded schematics at work and will post them soon. they are R36 and R59.

The shame is that I really like the amp and it's versatility, 2 1/2 channels, 2 master volumes, effects loop, 2x12 config.



Any other ideas? I like to learn thing by doing them myself so I will not be taking it to a "tech" (plus I'm WAY too "overly thrifty" (read,,, cheap).

T

Thanks for your time and consideration!!!

[mikeboone]

Did you check to see if you blew one of your speakers? That could give you a percieved 50% drop in volume on a 2x12 config.

Next thing would be to verify all your voltages. But I think if you had a significant voltage problem there would be a noticable change in tone in addition to the volume drop.

You would need a tone generator and volt meter to check the OT. Along with that you need to know the turns ratio of that OT. I worked on a Marshall with 3 EL34's and it was 20:1 so I would think they're the same. But you need to check into that.

With the power tubes out you can put the tone on the PRI (spkr out) and measure the voltage on the SEC (measure across pin3's of each socket). The voltage on the SEC should be 20VAC higher that the PRI. Some of the guys here in the forum led me to that a few days ago when I had a suspected bad OT.

[milkbone]

Speakers are good. I even tried with different settups and speakers. I don't have a tone generator but might be able to wrangle one up @ work. Thanks for info!

[mikeboone]

How does the amp sound? I worked on a Princeton Reverb recently that had lowered volume and a warbled sound. It turns out one of the tubes was not getting plate voltage due to a socket problem.

Make sure your tubes are operating correctly.

Do you have a way to check bias? Its one way to verify that a tube is drawing current. No current - no workie!!!

[milkbone]

schematic for the FA-60

This is the schematic

[milkbone]

I have a biasing meter. I'll hook it all up and report my find. Thanks! Mike

[milkbone]

Tube 1= 47 @ 526V
Tube 2= 39 @ 536V

They are both EH EL-34

It looks to me like they are ready to be replaced but what I don't understand is that I tried a "good" pair that worked fine in another amp and had the same results. I replaced the "good" pair back into their original and it worked fine.

If I use the standard formula 25 divided by 526 x .7 x 100 = 33.2
25 divided by 526 x .5 x 100 = 23.7

Numbers sure do look high. It is a "fixed" bias amp in A/B

[Enzo]

Take a cord and plug it into the effects send jack and the other end right back into the effects return jack. ANy help? If so, the return jack needs service.

Turn the reverb up some, then rick the amp to crash the reverb springs. Is that noise weak or is it strong like normal?

Flip the impedance speaker switch back and forth a couple times. Make any difference?

Plug your guitar into the effects return and play. Does that sound strong? No, it won;t be as loud as through the preamp.)

PLug a cord into the effects send adn connect that to the inpit of some other amp so youcan listen to what comes out the effects send. Is that weak, ir strong and normal sounding?

Trying to isolate the problem to a certain section of the amp.

[milkbone]

Roger Willco!

[milkbone]

Take a cord and plug it into the effects send jack and the other end right back into the effects return jack. ANy help? If so, the return jack needs service.

Turn the reverb up some, then rick the amp to crash the reverb springs. Is that noise weak or is it strong like normal?

Flip the impedance speaker switch back and forth a couple times. Make any difference?

Plug your guitar into the effects return and play. Does that sound strong? No, it won;t be as loud as through the preamp.)

PLug a cord into the effects send adn connect that to the inpit of some other amp so youcan listen to what comes out the effects send. Is that weak, ir strong and normal sounding?

Trying to isolate the problem to a certain section of the amp.

OK,,,effects loop is good, no difference with a cord inbetween.

Did the reverb thing, all is well

Flipped the OHm switch a few times, still good

Guitar straight in to return, kinda weak (like you said) but audible

FX loop send to another amp (to check preamp) sounded great.

Sounds like power section to me.?

[Enzo]

REverb all is well? I mean was the crash sound loud and strong? if so, the power amp is OK. We were not testing to see if the reverb worked, we were using the reverb as a way to insert a signal into the amp after the preamp. The reverb return is after the effects return but before the master volumes. If the reverb had the half power weakness you are chasing, then it points towards the power amp yes.

Get a CD player or something and plug into the effects return, or the preamp of some other amp and your guitar. If a nice strong signal makes a nice strong output from the speaker, then we would think the power amp OK. If it soulds half power then we look more.

The power amp needs both power tubes running. Make sure both pins 3 and 4 have B+ on BOTH tubes.

We might also suspect the op amp sections. Are both + and - 12v supplies up to spec?