Ampeg V4 w/6550

[Bernardduur]

Hey all!

Originally, my Ampeg V4 came shipped with 6550's. The former owner just put em in there and didn't care.

I was thinking about keeping the tubes but alter the amp slight so it would use these tubes normally. That would be altering the screen resistors, the bias resistors and the bias set.

My biggest concern is the heater-current; normally, a 7027 tube loaded amp uses 4x 0.9A. With 6550's they use 4x 1.6A. Is the PS of the Ampeg suited for this abuse? Can it deliver enough juice to the tubes and be able to keep this up day in day out?

I recently replaced my PS with a 240V version of it. It is the direct Ampeg replacement version. Dunno if it is different from the older PS'.

[jrfrond]

I determined a long time ago that you can do this freely, simply through experimentation. Install the 6550's, leave the amp on a few hours and see how hot the transformer gets. If it gets too hot to leave your hand on for 15sec or so, then your current draw is too high.

Many techs over the years replaced the disappearing 7027A's with 6550's with no ill effects to the amp. Ampeg amps of that era were nororiously overdesigned. It is rare to see one with a blown transformer. Of course, we can now get 7027A's again, so in most cases, it isn't necessary.

[Bernardduur]

I determined a long time ago that you can do this freely, simply through experimentation. Install the 6550's, leave the amp on a few hours and see how hot the transformer gets. If it gets too hot to leave your hand on for 15sec or so, then your current draw is too high.

Many techs over the years replaced the disappearing 7027A's with 6550's with no ill effects to the amp. Ampeg amps of that era were nororiously overdesigned. It is rare to see one with a blown transformer. Of course, we can now get 7027A's again, so in most cases, it isn't necessary.

Thanks man!

I determined something the same but I really like it to be sure . Don't wanna blow my baby!

As another thing; anyone ever enlarged the OT of the V4?

[Dave Curtis, dB AudioTech]

My '74 power tranny gets too warm for my taste with 6550s (but I had biased it pretty hot, too). 7027As aren't very different from good 6L6GCs; they just have more pins brought out to the base. The V4/VT22 doesn't use these extra connections, so you're good to go with (quality) 6L6GCs. FWIW, my VT22 still has OEM 7027As in it, even though I have a bunch of NOS RCAs...

[Bernardduur]

My '74 power tranny gets too warm for my taste with 6550s (but I had biased it pretty hot, too). 7027As aren't very different from good 6L6GCs; they just have more pins brought out to the base. The V4/VT22 doesn't use these extra connections, so you're good to go with (quality) 6L6GCs. FWIW, my VT22 still has OEM 7027As in it, even though I have a bunch of NOS RCAs...

Tnx!!!!!!

I'll update later when my unit arrives back!

I knew about the 7027's; I recently used JJ's 6L6GC's in my friends versions as they sound pretty decent!!!!

Small extra question btw; on a point the V4 starts distorting....... overdriving. Is this a cause of the preamp, the poweramp or both? Would it be for example handy to add a cleanosh boost in some FX loop to boost the poweramp to get more volume without OD'ing?

[Dave Curtis, dB AudioTech]

To be honest, the one time I turned it up loud enough to start distorting, everyone else in the band was completely drowned out, and birds started falling from the sky. OK, maybe the part about the birds is a fib, but seriously, I think it was my ears distorting, not the amp. That said, using it with a bass and a not-so-efficient cab, I'm able to turn it up enough to notice some distortion that reminds me very much of the bass in Grand Funk's "Black Licorice", for instance. You could try a clean boost, but usually that overdrives the preamp, unless used sparingly. Your sensitivity switches will play a role here, too. They set the gain of the first triodes on each channel.

[Bernardduur]

To be honest, the one time I turned it up loud enough to start distorting, everyone else in the band was completely drowned out, and birds started falling from the sky. OK, maybe the part about the birds is a fib, but seriously, I think it was my ears distorting, not the amp. That said, using it with a bass and a not-so-efficient cab, I'm able to turn it up enough to notice some distortion that reminds me very much of the bass in Grand Funk's "Black Licorice", for instance. You could try a clean boost, but usually that overdrives the preamp, unless used sparingly. Your sensitivity switches will play a role here, too. They set the gain of the first triodes on each channel.

Tnx!

I noticed in a small-ish bar that I need to turn my amp (as the amps of my friends) up well enough to get it distorted. Bass really does something with the efficiency . Big yes on the cabs but still not enough..... I would guess something extra volume would come pretty handy.........