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Ampeg V4B- the good, the bad, and NOS tubes

A

alexchavel

Feb 11, 2008
24
5
#1
Finally got my hands on a sweet early 70's v4b.

Been a while since I owned a vintage tube head, and this one is in particular is putting a smile on my face, especially through my 810 cab and berg nv215.

I had the amp recapped, and am now looking for tubes to upgrade, the amp had a misc hodgepodge of glass in there....

Pretty shocked at the prices for NOS tubes, so trying to make some wise choices...between these insane tube prices and the recapping that just happened I'm starting to remember the high cost of tube bliss, and why I've been playing SS heads for a few years!!

From what I know V1 tube is the most critical to the overall sound of the amp, so maybe a good place to put some bucks down on a good 12ax7 NOS Tube, and maybe the rest of the preamp section, then a good matched QUAD set of less expensive JJ's for output tubes?

Or bite the bullet and go all old school NOS Throughout? That would add up to almost what I payed for the amp!

Any opinions appreciated.
 
#2
Just because the tubes are old, don't just scrap them. You could already have some good killer old tubes in there. V1 is channel one, V2 is first stage channel two. The 6K11 I don't believe I have ever seem go bad and runs the tone stack. The real problem tubes are the 12DW7/7247's. JJ is the only one making a new direct pin 7027A. I don't know how the current quality is.
 
#5
Well, you have to buy a NOS 6K11. Good to have at least one spare, the price of those tubes are going up. Fliptops sells a 6AC10 as a substitute for the 6K11 for half the price. Haven't tried one. BTW, a 6K11 is like a 12AX7 and half of a 12AU7.

The 12DW7 is best to buy NOS rather than a JJ. A 12DW7 is half 12AX7 and half 12AU7.

The JJ 7027A isn't bad, but if you can afford NOS, they are nice to have.
 
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#6
Will definitely go NOS for all preamp ones...
But around 300$ for a matched quad of 7027 is hard to swallow...
I'm Finding matched pairs at decent prices, is putting two pairs of matched pairs a big issue? Is it the fact that two of tubes will work harder than the other two if not matched?
 
#7
If you want to save a little you can get a matched quad of odd brand 7027s from antique electronic supply for around $200. The new 7027s from JJ and Sovtek seem to hold up well for people. There are a lot of places still stocking old stock 12DW7s for decent prices. I Picked up a few 6k11s a few months back when they were still only $10-15 each but they seem to be around $30-40 everywhere now.
 
#8
alexchavel said:
Will definitely go NOS for all preamp ones...
But around 300$ for a matched quad of 7027 is hard to swallow...
I'm Finding matched pairs at decent prices, is putting two pairs of matched pairs a big issue? Is it the fact that two of tubes will work harder than the other two if not matched?
Click to expand...

Better to have a matched quad. The two tubes that are working harder will increase the total harmonic distortion. The noise will increase. The tubes should be balanced properly to avoid this.

Another solution is to have a separate bias for each power tube. This would require modifying the amp.

On the plus side, the V4B sounds good with the power tubes biased a little cooler. The tubes will last longer. Some people install 6550 tubes and they will last a VERY long time in a V4B.
 
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#12
B-string said:
Just be warned about the 6550 mod. Screen resistors should be changed and the heater current from 0.9A to 1.9A (new production) may require a separate filament transformer.
Click to expand...

Good point, you shouldn't just plug in 6550's. Some people do that though.

The heater current is a concern but it doesn't appear to be an issue with this amp. A lot of amps are run with 6550's and the transformer can take it.

As for the screen resistors, it is common to change the 470 1W screen resistors to 1K 5W. The 1K resistors should be used with 6550 tubes but people also make this change if they are running 7027A power tubes. The higher screen resistance sacrifices a few watts of output power but helps the tubes last longer.
 
#13
My V-4 is loaded with NOS tubes through and through. Didn't cost me an arm and a leg.

V1 - NOS Philips Holland I63 12AX7/ECC83 - $25 (eBay luck)
V2 - NOS RFT 12AX7/ECC83 - $20 (eBay luck)
V3 - NOS JAN Philips ECG 12DW7/7427 - $35 (fliptops.net)
V4 - NOS JAN Philips ECG 12AU7 - $15 (eBay luck)

Don't bother with 6550s, it's a big investment, hardly improves clean headroom and butchers a vintage amp. JJ 7027A are very good, they were in my V-4 when I purchased it and one of them was actually dead but I was able to get a quad of NOS Philips ECG 7027As from a friend. Also JJs seem to make Ampegs sound like Ampegs.

As for my 6K11/6Q11s I have a small collection of them that I got for no more than $25 each on eBay as well. That being said, I got a lot of my tubes from eBay. Only purchase from sellers who test their tubes and include their tubes NOS range and what tube actually tested. I.E. on a certain Hickok tube tester a brand new 12AX7/ECC83 will test 1250/1250. The Philips Holland I have in V1 that seller indicated in his ad the tube was tested 1400/1350 (beyond NOS, common with old tubes)
 
#14
beans-on-toast said:
The heater current is a concern but it doesn't appear to be an issue with this amp. A lot of amps are run with 6550's and the transformer can take it.
Click to expand...


My first V4 ran 6550s and the one I have currently runs 7027As. With the 6550s the amp would get hot almost to the point of not being able to touch the chassis after long rehearsals. The 7027A amp still runs a bit toasty but not quite as hot as the 6550 amp. The previous owner of the 6550 V4 had been running it that way for quite some time and unless he's modded it I'm sure the current owner of that amp has been as well. It sounded great in that configuration and I never used to worry about the heat, but having used this 7027A amp more frequently I wonder how much would be too much on a vintage amp.
 
#15
coreyfyfe said:
With the 6550s the amp would get hot almost to the point of not being able to touch the chassis after long rehearsals.
Click to expand...

The 6550 throws off more heat and the V4, especially with the back panel on, traps the heat. I wonder if you had the 1K screen resistors in your V4.

True about how much is too much on a vintage amp. Old transformers are more prone to stress from heat and higher current draw and the 6550 would push the power transformer harder.

I like the 7025A in the V4 because a 6550 makes it more like a lower power SVT. Some people like that and that's one reason why they run 6550's. Since I have an SVT, I would rather keep my V4B as a V4B if you know what I mean.
 
#16
I added a quiet 117V fan in mine, I also moved the OT forward to allow a little more space between the output tubes and OT. Didn't notice any heating issues. Rebias is absolutely needed with the 6550s. PT didn't get warm, but filament voltage did sag slightly at 6.1 volts with118vac mains.
 
#17
beans-on-toast said:
I like the 7025A in the V4 because a 6550 makes it more like a lower power SVT. Some people like that and that's one reason why they run 6550's. Since I have an SVT, I would rather keep my V4B as a V4B if you know what I mean.
Click to expand...

At the time I had my first one that's what I was looking for. I had an SVT-CL, and the 6550-V4 gave me that same sound in a smaller, sort of lighter, package with fewer tubes so I sold the SVT. Plus it was vintage so it must be better right ;). Now that I have a vintage SVT I like the differentiation of the 7027-V4. I wasn't as up on my technical knowledge at the time but when I had the 6550-V4 recapped my tech said he made sure everything was in place to optimize for the 6550s and added an adjustable bias so I can't confirm but would assume he did it right.

B-string said:
I added a quiet 117V fan in mine, I also moved the OT forward to allow a little more space between the output tubes and OT. Didn't notice any heating issues. Rebias is absolutely needed with the 6550s. PT didn't get warm, but filament voltage did sag slightly at 6.1 volts with118vac mains.
Click to expand...

I remember seeing the undercarriage of that amp in one of the V4 threads, it looked good.
 
#19
I play thru an ampeg vt22 combo with is the same as v4 but 212. I just put in a matched quad of sovtek 7027. They sound great and I push the amp pretty hard at times. Been 3 months so far with regular jams in a loud rock band and no issues. All my preamp tubes are still original I believe. When they go I'll be trying sovtek since the powertubes have treated me well thus far. Cost me around 150 for the quad shipped express from tubestore.com
 

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