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Tubes for my Ampeg V4B

D

doobeye

Jun 3, 2008
190
1
Moorpark, CA
wuss.bandcamp.com
#1
Blew a tube the other night at practice... yes I'm sad but i think this could be a good thing if i choose quality tubes to replace my amp with. I bought my amp used earlier this year and it had Sovteks so I definitely want to try some Groove Tubes next. All i know is with these new tubes i want to maximize power and have them last a long time. Right now my amp is rated at 100 watts but if i could get tubes that would increase it to even 120 watts, I'll be happy. Anyways, suggestions would greatly be appreciated. Especially if you too are an Ampeg V4B owner!

Thanks,
Chris
 
#3
kdogg said:
Hello Chris, you might want to check www.ampegv4.com. They have a lot of great info on tube swaps and biasing. I believe that swapping your 7027's, or 6L6's, for 6550's is the mod that will give you a bit more wattage. This mod is covered here: http://www.ampegv4.com/7027.php

Good luck in your search! You've got a great amp there! :hyper:
Click to expand...

No it will not give you more power but it could well end up blowing your power transformer.

Paul
 
#5
BassmanPaul said:
No it will not give you more power but it could well end up blowing your power transformer.

Paul
Click to expand...

The mod can definitely be done safely, and with no adverse effects to your V4.

Quotes from ampegv4.com, the site I referred the OP to:

6550 Series: This tube was a suggested "Upgrade" for V series after Magnavox took over. Go new old stock or Svetlana. (NOS will cost you $$$$). This is a great tube for BASS and Pedal Steel players. I am not so sure about guitar amps. Some guys like 'em, some don't! Remember the 6550 series tubes are a wide base design. The bear trap retainer clips will have to be removed. Simple enough, just drill out the rivet and remove the clip. Then re-revit or use a nut and bolt. Might be a good time to upgrade those worn sockets. (Antique radio has nice porcelain).

7027 tubes are rare and expensive, however, for under $3.00 one can modify these amps to accept 6550 or EL 34 tubes. The screen resistors are changed from 470 ohms. 1 watt to 1K 5 watts. If using EL 34 tubes, pin 1 has to be jumpered to pin 8. For 6550, R50 has to be changed to 82K. R49 sets the bias level. The plate resistors (R39, R40, R45, R46) are 10 ohms, so 0.4 volts =40 mA. When checking this voltage, the safest way to do it is to connect and disconnect the meter with the power off and capacitors discharged. (Modification taken from the Aspen-Pittman Tube Amp Book, with exception of biasing method). The recommended plate current for EL 34 and 6550 in most applications is 40-45 mA (then again, B+ is less than 450 volts). In the case of this amp with EL34's I would personally bias the power tubes around 30 mA. I received email from a person who tried 32 mA with EL 34's with no ill effects. I also read somewhere that EL34's should dissipate 15-18 watts at idle (the math for 545 volts of B+ equates to 30 mA of plate current).
 
#6
The mod is definitely quick and easy, and it's been done in my amp and I have not had any problems. Furthermore, I bought the amp from someone who was running it with Sovtek 6550s without modification and my tech said the amp was running fine, there was no reason to worry about the transformers.

But, as Paul said, running 6550s in it does not give you a boost in output wattage (as far as my ears can tell at least).
 
#7
not meaning to nitpik, but I think Groove Tubes is actually making some of their tubes, (I could be wrong) supposedly they have some old GE equipment, I haven't heard much about them.
Link Removed
 
#8
doobeye, Ampeg rated those amps at 100w, but modern measurements put them at 120w already. And really, you won't hear any difference at all between 100 and 120w. It's not a big enough difference to matter except ever so slightly. OTOH, you had a goal and you accomplished it without costing you a cent!

I would suggest NOS tubes, but NOS power tubes can be ridiculously expensive. But they will usually last way longer than new tubes, though new tubes are better than they used to be when they first moved to Russia and China. Problem is you just never know...
 
#11
I've got a V4B and I just had it retubed & recaped, ....the shop had Sovtek 7027's in stock and that's whats in the amp now, my next step is to load a set of JJ 6l6GC in them, and see if there is a differance ( JJ 6L6GC can be had for not much money ) ... I did locate a quad set of GE 7027's and they were way too pricey ( $300 ) ...one note, on this amp you really need fresh inverter tube (12AU7 ) and a driver tube ( 12DW7 or if your not going to use the preamp out, you can use a 12AX7 ), to get a punchy tone/sound, also the compactron tube 6K11 is the tube for the tone circuits, when I changed it out, I noticed a slight tightening in the sound
 
#13
i think that the best tubes to run in an older V4 are NOS Philips 7581A's. they are capable of the same output as 6550's (35 watts ea), fit the tube sockets properly (6550's don't!), don't require ANY modifications, sound the best (to my ears), and will last a VERY long time.

basically , they are an extremely robust, mil-spec 6L6GC that handle high plate voltages.

all three of my V4's tested at 108 RMS watts (clean), but they 'feel' like alot more than that.

2 cents..............
 
#14
#15
kdogg said:
The mod can definitely be done safely, and with no adverse effects to your V4.

Quotes from ampegv4.com, [/I]
Click to expand...

I edited for brevity. All your quotes are talking about plate dissipations and they are correct as far as they go.

I'm talking about the difference in heater current draw. 6L6GC/7027A pull 0.9A each. EL34 and 6550 pull 1.5/1.6A each depending on who makes it. That's 0.6A per tube difference or 2.4A more for the quartet. 3.6A increases to 6.0/6.4A depending. That IS a significant difference over what the transformer was designed for, heading on towards double. To do the switch safely a secondary heater transformer should be provided.

Paul
 

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