tube replacement for ampeg v-4b and svt-av to reduce preamp distortion?

jpc · #1 03-20-2010, 03:12 PM

hello everyone,

i bought a late 70's ampeg v-4b some weeks ago to finally have a chance to hear what the hype is all about. so far i'm really impressed with the tone. it's noting compared to the svt-av i usally use. what i don't like is the distortion that sets in at around 11 o'clock. that is why i want some advice on how i could replace tubes to avoid having distortion at that early stage. i don't have problems with a nice creamy overdrive the louder it gets but not that harsh distortion. my current tube setup is:

4 x 7027a (national electronics)
1 x 6k11 (magnavox)
1 x 12dw7 (national electronics)
1 x 12au7 (unmarked)
2 x 12ax7 (unmarked)

i read something about changing the 12ax7 to a 5751 a get more of what i want. i'm playing rickenbacker 4001 & 4003 through an ampeg 810 if that matters. what do you suggest? which tube(s) should i replace?

basically the same question i have for my ampeg svt-av. the preamp distortion is nasty and i would like to have it smoother with less distortion. tube setup is:

6 x 6550we (sovtek)
2 x 12au7 (elektro harmonix)
1 x 12ax7wa (sovtek)

do you have recommendations for this amp as well?

there is just one more question

does any of you know where i can get a cover for the v-4b, not a case but a flexible, resistant dust cover?

thank you...

JimmyM · #2 03-20-2010, 03:49 PM

the best you can do is lower the gain structure, which whether clean sound ends at 11:00 or 3:00, it'll still give you the same result. ignore the knob positions and turn the gain down to where it sounds usable to you. that's pretty standard for ampegs.

jpc · #3 03-20-2010, 04:01 PM

Quote:

Originally Posted by JimmyM

the best you can do is lower the gain structure, which whether clean sound ends at 11:00 or 3:00, it'll still give you the same result. ignore the knob positions and turn the gain down to where it sounds usable to you. that's pretty standard for ampegs.

what do you mean by "gain structure"?
the difference between 11 and 3 is that i have more volume at 3. turning down the volume to a usable sound might work in the rehearsal space but it won't when playing live.

JimmyM · #4 03-20-2010, 04:19 PM

Quote:

Originally Posted by jpc

what do you mean by "gain structure"?
the difference between 11 and 3 is that i have more volume at 3. turning down the volume to a usable sound might work in the rehearsal space but it won't when playing live.

you only think there's going to be more volume if you change tubes, but there won't be. you'll just make everything quieter. 11:00 will be very quiet, and 3:00 will be where 11:00 is now. just ignore the knob positions. they mean nothing in relation to how loud your amp can go. it's still going to distort at the same gain/volume levels regardless of knob position. you'll just have a different knob position.

johnk_10 · #5 03-20-2010, 04:19 PM

i'd replace the 12AX7's with 5751's in both amps, and that should get you closer to what you want.

username1 · #6 03-20-2010, 04:20 PM

I think your problem isnt the tubes. I have a 12ax7 in one channel and a 5751 in the other of my v4b. Neither channel will make the amp louder before distortion. They are only 100 watts and run out of headroom in the power section quickly. I found i prefer the sound of the channel where i have a new tungsol 12ax7 as opposed to the vintage 5751 i have in the other. The 5751 might work well in the svt though for a smother distortion. You will have to live with the distortion of the V4b because i dont believe they have enough power for a good bottom end as opposed to the svt unless you are running at low volume levels.

johnk_10 · #7 03-20-2010, 04:24 PM

you are correct that neither preamp tube will make the amp louder-it has its limits, but a 5751 should give you a little more preamp gain 'adjustment room' before the preamp distorts.

username1 · #8 03-20-2010, 04:43 PM

Quote:

Originally Posted by johnk_10

you are correct that neither preamp tube will make the amp louder-it has its limits, but a 5751 should give you a little more preamp gain 'adjustment room' before the preamp distorts.

I totaly agree but find my distortion seems to come more from the power section not having the balls of my svt and crapping out on the low notes alot sooner. I can turn the gain up a bit more with the 5751 but cant get any improvement in overall volume before distortion. I tried the 5751 in my svt and liked the result of it in there. If you have a hard time finding a good old 5751 pm me. I have a few i found at an army surplus store new in the box from 1963.

jpc · #9 03-20-2010, 05:12 PM

Quote:

Originally Posted by username1

I totaly agree but find my distortion seems to come more from the power section not having the balls of my svt and crapping out on the low notes alot sooner. I can turn the gain up a bit more with the 5751 but cant get any improvement in overall volume before distortion. I tried the 5751 in my svt and liked the result of it in there. If you have a hard time finding a good old 5751 pm me. I have a few i found at an army surplus store new in the box from 1963.

thank you for the offer, but i live here in the old world and shipping would probably be a lot. i found the philips jan 5751 in a tube store. i think that's a good one?

so would it be possible to use a smoother preamp tube (like 5751) AND better power tubes (upgrading to 6550?) to get more overall volume with less distortion but the characteristic tone of the v-4b?

username1 · #10 03-20-2010, 05:24 PM

so would it be possible to use a smoother preamp tube (like 5751) AND better power tubes (upgrading to 6550?) to get more overall volume with less distortion but the characteristic tone of the v-4b?[/quote]

I believe your not going to get much of an improvment being the amp is only capable of so much. If you have 2 speaker cabs i would power one with the v4b and use a seperate power amp for the other with the pre out signal from the v4. It probably wouldnt cost any more than upgrades but will defently get you the volume you need.

username1 · #11 03-20-2010, 05:36 PM

I just read your profile and saw you are using an 810 cab. If it is not an older one it should have 2 inputs to power each set of 410's in it. You could just power half the cab with the v4 and the other with another power amp. Any solid state head with a pre in would also work for powering the other set of 410's. The beauty of an old v4b is that it has 8 ohm capability which would match perfectly for one set of 410's.

jpc · #12 03-20-2010, 05:51 PM

it's an older 810 with just one input. also, i was hoping to finally have an amp to fit all my sonic needs. having an extra power amp to carry around besides the already heavy ampeg armada is just too much for me

username1 · #13 03-20-2010, 06:00 PM

I totaly understand. It was just the only way i could think of to get the volume you needed and didnt want to see you spend alot of money for an end result that wouldn't make alot of difference. I had the same problems with my v4b and found there is only so much you can do other than the power amp trick. I have done that before with great results but it was more equipment to haul around so i just use my svt now and the v4 for low volume gigs.