Ampeg V4 Issue

[Adam79]

Hi. I'm looking into buying a broken V4; the price is too cheap to pass up. Anyways, the story goes that the owner replaced one of the 7027 tubes with a 6L6. An hour into playing, the amp broke down. Now it doesn't even turn on. Can switching in a 6L6 cause this to happen? I know that some variants of 6L6 can be used as a substitute, but to the best of my knowledge, the 6L6 isn't one of those variants. Please Help!

Thanks,
-Adam

[chillerthanmost]

I put Sylvania 6L6GC tubes in mine (when I had it) with no problems. It sounded way better than the muddy JJ 7027's in there. It could have been bad distribution of power if only one was replaced or just a bad tube which could cause the fuse to blow. If so, it's a very easy fix. Take a new fuse with you when you go look at it, try it out and see if it turns on. If you happen to have a set of 6L6GC's you can put them in just to check if it works. Even if it's just two. Be sure to finalize the final asking price before and ask to swap those things before you decide to purchase it.

[sharpshooter]

As a V4,,(well, a cut down VT22), owner, when I got it, it sounded bad, tech did a lot,,well worth it,,monster amp.
With the plate voltages running around 540>570, only the real high strength versions of the 6L6 family will hold up.
I know there's a lot of flack over some of JJs tubes,, but the 6L6s they have hold up in V4s. This place has most of the answers for the V series amps.

http://www.ampegv4.com/index.php

[chillerthanmost]

From my experience, V4's eat JJ'a like no ones business. It ate up my JJ's in a year and same with Ruby's. I had Sylvanias in there longer than any of the others and they also sounded best. Either way though, to the OP, it will work with 6L6GC tubes. If you're lucky, it's just a fuse and you can replace the tubes. How much is the seller asking for?

[riff1006]

Aren't the 7027s wired different than the 6L6s at the tube sockets? I'm thinking they aren't direct replacements without rewiring?

[chillerthanmost]

Originally Posted by riff1006

Aren't the 7027s wired different than the 6L6s at the tube sockets? I'm thinking they aren't direct replacements without rewiring?

You sir, are correct except the v4 doesn't use the extra pin. It's a dummy slot on the tube socket. Besides the pin, both tubes are identical. V4's will work just as good with a 6L6GC. The only reason I'd recommend a "good" tube is because of the plate voltage being high. It will eat up lower quality tubes.

[sharpshooter]

^ The 7027 does have a diff pin-out,,but, the ampeg curcuit does not use the pin on the 7027 that is diff.
When the V series curcuits were designed, the existing 6L6 tubes,(at that time), would not take the plate voltage,,the 7027 was a higher rated, (both in voltage, and in watts), tube, and so was used.

[Blue Strat]

The only sub you should use is the JAN Philips 7581A which sounds great and holds up well.

As for the current condition of your amp it's impossible to say without more information and even then, it's likely that only an amp tech can sort it out.

BTW, what EXACTLY does "the amp broke down" mean? Does it light up at all? Is the fuse blown?

[sharpshooter]

When my V4 was in the shop, the tech told me that Ampeg uses a "capacitive-divider" bias scheme,,and it can get out of whack if any components drift off spec. This can, (and will), cause all sorts of problems pertaining to the power tubes.
With any of these old V amps, having the bias curcuit checked is a good idea, and a tech can, for only a few $, and a little bit of time, can install a "trim pot" in the bias curcuit. If you look at a V4 schematic,,you can go insane,,they are comlicated, and everything needs to be "just so".
When it is, they are quite reliable.

[sharpshooter]

Originally Posted by Blue Strat

The only sub you should use is the JAN Philips 7581A which sounds great and holds up well.

There is one quad of those tubes on the bay,,bin price,,850.00$
Might you have some for less$?

[Stringrazor]

a little OT....

As a teen in the early 70's, I bought a used V4 for $225 - a LOT of $ for me then. It was as loud as it was heavy. Through the years I'd have strange problems where it would sound like I was hearing only the reverb circuit. The 'solution' I found was to blast a power chord at full volume, which was near lethal. So, I'd pull the speaker connection and then do it. Sometimes it would work, other times I'd blow the fuse and as it turned out some diodes too. My dad gave me heavy duty mil-spec diodes and I learned to replace them quickly on a break if I had to. No tech was ever able to find the "sounds like reverb circuit only" problem (cold solder joint???). I finally traded it in @ GC, Sherman Oaks in 1999 for $300 credit. It sat in the used gear section for months and I'd visit it every now and then. It had a replacement power switch with plastic lever. Wonder who has it now?

[Blue Strat]

Originally Posted by sharpshooter

There is one quad of those tubes on the bay,,bin price,,850.00$
Might you have some for less$?

Sure. You can click on the link below and see.