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Ampeg V4-B: Any mods to make more output?

#41
In the later Linden NJ production ( any that use a 6AN8 tube ) there are no changes needed to use 6550 in these amps. This isn't according to me, Its from the Ampeg manuals and schematics from the era.

As to how to use 6550s in the earlier Linden NJ production ( amps using a 6K11 tube ) , Change the screen resistors to 1k at 5 watts. Change the tube retainer clips to allow for the larger base. Check idle current and reset bias if needed. I've run mine this way for 10 years gigging every weekend. No problem with the PT. If you are still worried about the added filament draw at the PT what you do is disconnect the filament feed for the last two power tubes, add a 3.5 amp 6.3vac transformer to the chassis to feed to last two tubes. add a pair of 100 resistors for the hum balance and be happy. Its also a good idea to avoid the coke bottle style 6550 as they can rattle against the transformer. The straight side GE style 6550 works just fine but, IME it doesn't bias quite the same as old GE 6550 so, do check the idle current.

As to the current SLM production, I haven't dealt with them. I have no comment.

It is possible to get 100 watts out of a pair of original GE 6550 but it is done at a price. the price is tube life. I had a West Grande guitar amp years ago that did exactly that. It ate GE 6550 at a rate of a pair about every 4- 6 months. Remember too that back in the day, tube makers underrated the specs for the tubes by 30%. The 6V6 has a rated maximum plate voltage of 350 volts yet the fender deluxe reverb ran them at 420 volts or 30% over. Most current production tubes don't have the 30% headroom the old ones did. To get 100 watts from a pair or 6550s you need to push the plate voltage up to almost 700 volts. The winged C 6550 are rated up to 680 vdc. To do this with a V4 you would need the change the PT and the OT and you would be pushing your luck with current tubes. I have a small stockpile of GE6550 that I use with my SVT. I don't know what I'll do when they are gone. I don't trust current production tubes above 75 watts a pair output.

Archie
 
#43
archieaa1 said:
In the later Linden NJ production ( any that use a 6AN8 tube ) there are no changes needed to use 6550 in these amps. This isn't according to me, Its from the Ampeg manuals and schematics from the era.

As to how to use 6550s in the earlier Linden NJ production ( amps using a 6K11 tube ) , Change the screen resistors to 1k at 5 watts. Change the tube retainer clips to allow for the larger base. Check idle current and reset bias if needed. I've run mine this way for 10 years gigging every weekend. No problem with the PT. If you are still worried about the added filament draw at the PT what you do is disconnect the filament feed for the last two power tubes, add a 3.5 amp 6.3vac transformer to the chassis to feed to last two tubes. add a pair of 100 resistors for the hum balance and be happy. Its also a good idea to avoid the coke bottle style 6550 as they can rattle against the transformer. The straight side GE style 6550 works just fine but, IME it doesn't bias quite the same as old GE 6550 so, do check the idle current.

As to the current SLM production, I haven't dealt with them. I have no comment.

It is possible to get 100 watts out of a pair of original GE 6550 but it is done at a price. the price is tube life. I had a West Grande guitar amp years ago that did exactly that. It ate GE 6550 at a rate of a pair about every 4- 6 months. Remember too that back in the day, tube makers underrated the specs for the tubes by 30%. The 6V6 has a rated maximum plate voltage of 350 volts yet the fender deluxe reverb ran them at 420 volts or 30% over. Most current production tubes don't have the 30% headroom the old ones did. To get 100 watts from a pair or 6550s you need to push the plate voltage up to almost 700 volts. The winged C 6550 are rated up to 680 vdc. To do this with a V4 you would need the change the PT and the OT and you would be pushing your luck with current tubes. I have a small stockpile of GE6550 that I use with my SVT. I don't know what I'll do when they are gone. I don't trust current production tubes above 75 watts a pair output.

Archie
Click to expand...
Thanks Archie, That's exactly what I was wondering , whether the PT had to be upgraded to pull off this mod. Which to me would make it not worth doing.
 
#45
I was playing a little today and had my SVT-II sitting on the floor partially apart.. As the shiny 6550 tube tops were gleaming I got the wild idea to try out the 6550's for a short while in my early 70's V4.. I figured I love the tone of my v4 and I love the tone of the SVT, so why not? Granted it is not modded for 6550's as it a 6k11 model, but I was only going to do it for a short bit at low volumes.

Swapped out the JJ 7027's and in with a quad of 6550's and powered it up... Jammed out a few songs on my Jazz through a 410HLF.. All I can say is........ WOW!!!! I fell in love with the v4 all over again... The 6550's seemed to add a much warmer and fuller bottom end and such a great tone! And to think these are cheap Groove Tube 6550 c's... Imagine what could be if I had some good 6550's!

Time to pick up some supplies and pull out the Weller.


One thing I have to add though... With my unmodded v4 and the 6550's there was a definite temp increase on the chassis at the power tubes. I dont have my temp gun so I wasnt able to get a comparison.
 
#46
I run my V2 (half the power of the V4B) with a 2x15 and 8x10. No volume problem there :D


IMG_7028.jpg
 
#48
I will never part with my V-4 (1972 Magnavox)!! It sounds amazing and still has tubes from 1984 (GE 7027As) and has the 6K11. This amp is ultra reliable and heavy and hangs over the edge of most cabs.
On stage I use an Ashdown ABM500 with a VT-Bass into a Henry 8x8 and this has "almost the feel" of the V-4.

The V-4 stays in the house, but I would not hesitate to take it on any gig if I needed to. I have it running into a 2-15 Fender cab with Celestion bass 15s.

I would buy another for the right price (real cheap) just to have it.
 
#49
I have my (197?) Magnavox running a quad of KT88s and find that it runs a little hotter but the sound is much fuller. Overall headroom isn't much difference. I also built a head cab that is about an inch taller and better vented than the original to aid in air circulation.

- J -
 
#50
j_rod said:
I have my (197?) Magnavox running a quad of KT88s and find that it runs a little hotter but the sound is much fuller. Overall headroom isn't much difference. I also built a head cab that is about an inch taller and better vented than the original to aid in air circulation.

- J -
Click to expand...

i'd add a fan blowing on the power transformer to try and cool it down.

Paul
 
#51
mcrracer said:
I have over 35 years experience in designing and building tube amps. I was trying to see if he was just being flip. Doing it right is a major undertaking especially if the original PT is not quite up to snuff.
Click to expand...

Snap my brother snap. :)

There's altogether too much advice for players to open up and mess with their tube amps with no knowledge of what they are doing!

So many people think that all they have to do is install larger, more powerful output tubes into an amp and they'll get more power. One poster awhile ago claimed 200W out of his V4 after such a mod. As we know that's impossible.

Paul
 
#52
BassmanPaul said:
Snap my brother snap. :)

There's altogether too much advice for players to open up and mess with their tube amps with no knowledge of what they are doing!

So many people think that all they have to do is install larger, more powerful output tubes into an amp and they'll get more power. One poster awhile ago claimed 200W out of his V4 after such a mod. As we know that's impossible.

Paul
Click to expand...

Like i said, you can swap tubes all day.. but it doesn't matter if the transformers aren't up to Snuff!

If people read stuff more carefully, or did a decent amount of research then they'd know it. But there isn't always much instant gratification with learning how to do stuff properly. :rollno:
 
#53
Came across this thread, had to sign up. :)

Not mentioned yet...

KT77's

I purchased an old V4-b last summer. It was modded before I got it. Something like jump pins 1 to 8 in the tube socket. Makes it able for EL34's or KT77's. This one has four JJ KT77's in it.

I can't tell ya how it compares, but it seriously puts out.

I just love this amp. I have gigged the hell out of. Love it. I use it with a 4 ohm 2 X 12 cab.

I used SVT's before I got it and was afraid it might not be loud enough. :D
 
#54
EL34s are a proper pentode and need their suppressor grids, G3 (pin 1) externally connected. The easiest way to do this is to strap pins 1 and 8 (cathode), better yet is to connect G3 to the negative bias supply.

The KT77 has the same drawback as the 6550 et-al in that its heater draw is half an amp more per tube than the PT was designed for. A secondary heater transformer is the remedy for this.

Paul
 
#57
BassmanPaul said:
EVERY time you replace the power tubes the bias and the quiescent current through the tubes should be checked.

Paul
Click to expand...

+1.
the V4 and V4B don't have a bias pot, so you have to often change a resistor or two to get the output tubes to run at their individual spec.
 
#59

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