ampeg v-5 not loud at all

[ddm]

Im having a problem with a v-5..I know with my 6550 marshall i cant put it past 2, its deafening..

My v-5 that that i just picked up, put in new tubes and biased, i can max out the master and its still not as loud as my marshall on 2

has anyone seen this issue with the mti era ampegs? why wouldnt it be loud?
any help would be appreciated...

Thanks
Dennis

[52 Bill]

I haven't seen that many V-5's, so I don't know of any systemic issues with them. I know a few of us have seen dead power transformers, but nothing else comes to mind.

There are a million things that could cause your amp or any amp to lose volume. A few that come to mind are dirty loop contacts, dirty or loose tube sockets, dead or weak tubes, off value caps or resistors, low B+ voltages, bad pots, bad speakers, etc.

First check all of the simple things and then move on to the tougher ones. Get a copy of the schematic, it'll help.

[ddm]

Contacts are all clean.. Power trans is ok.. What i dont know if the output trans is ok because of the low volume.. I can dime the preamp and master and my marshall is louder on 1 than this on full!

Sockets were cleaned tubes are new.. b+ is 465 for each 6550
each tube has 55ma bias current
pots look good..
filter caps all check good on my esr meter..
tried all output impedances... all same volume level

It must lie somewhere after the master volume on the schematic... it seems as if the phase inverter isnt amplfying it enough... or trans..

Is there a simple test for the OT?

Thanks!
Dennis

[52 Bill]

each tube has 55ma bias current

55mA per tube? No wonder why the power transformers are stressed.

It must lie somewhere after the master volume on the schematic... it seems as if the phase inverter isnt amplfying it enough... or trans..

The phase inverter is standard Fender/Marshall circuit. Are all of the voltages in normal range?

Does the signal sound overdriven but quiet? If the problem was in the PI, I would imagine that with the volume cranked that pre-amp would be clipping like crazy if it was processing the signal normally. Have you checked the gain switch at the input of V2?

Is there a simple test for the OT?

The simplest is substitution.

Inject a signal into the input and trace it through each stage and see where it dies or doesn't get amplified. Use an oscilloscope or ac voltmeter or a signal tracer to check each stage.

[ddm]

Im going to check the voltages at the pins now..
I have a 2203 voltage diagram, this amp should be the same..

The signal is overdriven... theres just no volume with the master... it goes to 3 before you can actually hear it louder than a normal conversation.

The gain switch is ok.. The bright switch doesnt really sound like it does anything but i dont think it would have an affect on volume..

Thanks
Dennis

[52 Bill]

The bright switch is a bypass type, so it will not have any effect when the volume control is at 10.

Try unhooking the lead from the master into the power amp, and either feed the pre-amp signal out to another amp or feed in a signal from another source into the power amp. This way you'll know which side is working.

[ddm]

Some wierd voltages...

v2 pin 8 is at 81 volts... should be around 150
v3 pin 1 -s at 61, pin 2 is at 57 (should be no voltage there)
pin 3 is at 55 (should be 18.5)
pin 6 is at 240 ( should be 195)
pin 7 is at 42 ( should be no voltage)
pin 8 is at 56 (should be at 18.5)

maybe the .022 coupling caps are done?

that wouldnt explain the low cathode voltage on v2b though

[ddm]

v2 voltages are ok now... sprayed the socket again...


now its just off on v3

[52 Bill]

v3 pin 1 -s at 61

I would expect a lot more voltage here, more like what is on pin 6. Are the two plate resistors ok?

pin 2 is at 57 (should be no voltage there)
pin 7 is at 42 ( should be no voltage)

This could be a problem. Check all of the PI resistors and especially the ground connection on the 4k7 resistor.

[ddm]

Would you believe i had 2 bad tubes?

The initial one, v3 and the one i replaced it with was bad too..

The third one...a nos phillips did the trick..

I fell like a retart but what are the chances of that, 2 bad tubes in a row..

its all working now and its deafening on 2...

Bill thank you for your help..!!

[52 Bill]

I hate when that happens!

Did you check the socket? You had mentioned a problem with the socket for V2 earlier. I know that sometimes these new manufacture tubes have smaller metric sized pins, and NOS US made tubes have bigger pins that will make a marginal socket work. Just a thought.

Well anyway, glad to hear that it's back up and running.

[ampegman83]

do you have pics? i've never seen a V5 and id love to. Ive also never seen a V3 for that fact, but i know they are basically b-25's.

[Dave Curtis, dB AudioTech]

Did you check the socket? You had mentioned a problem with the socket for V2 earlier. I know that sometimes these new manufacture tubes have smaller metric sized pins, and NOS US made tubes have bigger pins that will make a marginal socket work. Just a thought.


All the preamp tube pins I just measured (EH, Shuguaung, Mullard, GE, Philips and Matsushita) are all .035" with the exception of the EH, which was .0345". I haven't much of a problem with different size pins, but the end-dress on new (power) tubes pins can be horrible, causing them to fetch up while installing them. Most have no taper at all on the tip.

The pin-size problem I ran into was the new EH 7868 pins being .015" bigger than the old ones (.050>.035). They went in, but they didn't want to. If I ever want to put old ones in the amp, I'll definitely have to retention the sockets; they won't hold the pins at all. I told M. Matthews know about it, but I don't know if the current tubes have the right sized pins.

[52 Bill]

Thank you Dave, I stand corrected! (Sit actually)

I've never bothered to actually measure the pins, but just seem to remember this as being a problem back when the Chinese and Russian tubes started to appear on the market.

Thanks again.