5150 III Volume Problem

[plexi50]

I have a Peavey 5150 III with low volume on channels 1 & 2. Not a lot of volume for a 100 watt amp. Channel 3 is working fine with insane amounts of volume. I have swapped out all of the the preamp tubes and now channels 1&2 are a bit louder but still not as loud as i would expect them to be. I checked the filament voltages,DC on V1 & V4 and they read good at 6.00+ VDC. But all of the AC filament voltages are reading 5.18 VAC & less (fluxuating drift)

6L6GC tube filaments are reading 5.14 VAC across pin 2 & 7

Heater supply from transformer leads pulled from board reading 6.20VAC with no load. Under load 6.07VAC

At times i think channel 1 & 2 are louder than they were a few minutes earlier. Could this volume issue be filament related. Sort of looks like it. I dont have any experience with the 5150 III that i can recall right now. Has anyone else had any of these issues with lower than average volume and lower than 6.00 V A/C filament voltages? I am measuring across from pins 4&5 to pin 9 VAC

The relays are functioning (switching) from channel to channel

[six el six]

I have a problem w/a Carvin Legacy right now that's similar to what you're describing..

Sluckey's troubleshooting advice might apply to your situation as well.

See the Carvin Legacy thread.

[plexi50]

Thanks SIX el SIX. I have been reading your post for a couple of days now with curiosity. I did not expect to get a 5150 in tonight with the very same issue. Small world. I got the same voltage increase results here pulling the 6L6GC power tubes. I have a PT to tack in tommorrow and see what happens

[tubeswell]

leaky coupling cap somewhere?

[plexi50]

leaky coupling cap somewhere?

How could a leaky coupling cap effect the filament voltage? Tube current draw?

[tubeswell]

I wasn't thinking about filament current - I was thinking about bias voltage. And you said that the other channel was okay. So I guessed (maybe wrongly) that the problem was coming from somewhere other than the output stage (altho' 5.1 is on the low side for the heaters).

[stratele52]

Leaking cap could drop signal . Nothing to do with low heater supply. Better to check your B+ voltage on preamp's tubes. Low B+ could mean low power .

What do you mean with ; " ....all of the AC filament voltages are reading 5.18 volts and less...."

  "...heater supply ...under load 6.07 VAC

Which is the right mesurement  ?   Anyway I don't think 5.18 volts mean low power.

??????

[stratele52]

Yes tubeswell , if some channels work fine, output tubes stage are Ok. Same as Phase Inverter.

[plexi50]

Leaking cap could drop signal . Nothing to do with low heater supply. Better to check your B+ voltage on preamp's tubes. Low B+ could mean low power .

What do you mean with ; " ....all of the AC filament voltages are reading 5.18 volts and less...."

  "...heater supply ...under load 6.07 VAC

Which is the right mesurement  ?   Anyway I don't think 5.18 volts mean low power.

??????

What do you mean with ; " ....all of the AC filament voltages are reading 5.18 volts and less...."

There are 2 DC filament powered tubes V1 & V4 whaich read 6VDC
All the other tubes in the amp are using A/C filament voltage

Heater supply from transformer leads (pulled from board) reading 6.20VAC with no load
Heater supply leads put back (on the board) Under load 6.07VAC
This measurement was taken at the supply leads themselves

But if i take measurments on the power and preamp tube pins i was getting 5.18 VAC and less (drifting) last night

This morning i am reading 5.02VAC with power tubes removed from the amp and 4.22VAC with the power tubes in the amp (under load)
This is measured across from pin 2 to pin 7 of the power tubes

[plexi50]

I just took cathode voltage readings and they are all within the schematic voltage numbers

[sluckey]

Heater supply leads put back (on the board) Under load 6.07VAC
This measurement was taken at the supply leads themselves

But if i take measurments on the power and preamp tube pins i was getting 5.18 VAC

Sounds like a bad (resistive) connection. Check connectors, board traces, solder joints, links, etc.

[tubeswell]

Another possibility is a bad/partially-shorted filter cap in the DC supply for the heaters, which could be loading down the heater supply. When you say that you measured the filament circuit unloaded, did you mean with the tubes out, or with the PT disconnected from the rest of the amp?

[phsyconoodler]

I agree with sluckey. A bad connection,cold solder joint,bad ground is likely the cause.
  anything to do with the heater circuit in general needs to be checked and cleaned,re-soldered,grounded properly.
  I would have guessed the DC heaters would cause issues not the AC heaters in those amps,but? ........   

[stratele52]

I agree with slucky.

I never see this amp. If this amp have few connectors this could be all of your's problems.  Low heater voltage and week sound.

Can you show a picture of the inside of the chassis  ?

[plexi50]

Man this thing has nothing in common with the Peavey 5150. This amp is made by Fender in Mexico. Ok heres what i have found:

(1) The filaments for the preamp and power tube boards are hard wired from the filament fuse on the power board
(2) I see no voltage regulator in this amp for the A/C portion of the heater filament voltage other than the filament caps
(3) I have to remove the PS board to get to the filament caps just yet. If they are not the problem then the PT filament winding is shot
(4) I pulled the filament wires feeding the preamp board and there is virtually no change or rise in filament voltage on the power tube board
(5) The schematic for this amp is worthless as far as the power supply goes
(6) I am blind and i just got a pair of those jewlers magnifier lens that you wear on your head. Amazing vision
(7) Getting interesting now! Next*

(8) I pushed down on the filament fuse to see if it was making a good connection. The fuse was very hot. The voltage rised to 5.92 / 6.00VAC and is solid for 30 minutes. And at that point the fuse became cool to the touch and not hot at all. I touched the fuse again and the voltage dropped. It looks like i need to remove the PS board and more than likely resolder the fuse and filament push on terminal for the entire amp

I cleaned and tightened the fuse holder and fuse but this is not the problem. That would have been nice

Here are some pics of this amp. I didnt know that Fender even made the 5150III. I thought this was a Peavey product




 

[sluckey]

resolder the fuse

definitely.

[stratele52]

Thank's fot the good pictures. This kind of amp , pcb board  with lots of connectors is not easy to fix . When they get old mean lots fo trouble / bad connexions ?

So it is a fender !

[plexi50]

AMEN* Working fine now with a solid 6VAC on all power and preamp tubes. Man you need ear plugs with this amp. At least it has hardwired filaments unlike the Crate BV120 amps. Those amps are terrible using small heater traces. Thanks for all your help people. I learned something new again.

Get some of these magnifier glasses if you are having a harder time seeing work up close these days. Solder joints now looks like mountains and valleys.

[stratele52]

Good news..

I have those magnifier glasses sinceI saw some pictures of Leo Fender using them all the time. These are very helpfull tool.

[Ritchie200]

So what was the problem?  Did you re-solder the fuse holder?

Jim

[plexi50]

So what was the problem?  Did you re-solder the fuse holder?

Jim

The problem was a poor solder connection on the heater fuse cups under the board. + the fuse holder itself didnt have enough tension to grab the fuse tightly. By the way that fuse was rated at 12 amps. Ive seen 6amps here and there but never a 12 amp factory tube amp fuse. The schematic does not show the fuse or it's rating. But the owner has never had it opened up since he bought it new

[Ritchie200]

Hay Plexi50,

Schemo shows F1 heater fuse as a 12amp slow-blow. 

http://support.evhgear.com/schematics/EVH_5150III_AmpHead_Schematics.pdf

This is all great info as I get these things (5150's) all the time.

Thanks!
Jim

[plexi50]

Thanks Jim! Thats a nice full detailed schematic. The one i have is one page and does not show the power transformer