Early 70's V4b best tubes

jerkass9879 · #1 10-05-2011, 07:05 AM

Who has experience with these heads and who can recommend a decent set of tubes. I've used SED's, JJ, and electro harmonix. I loved the sound of the SED'S but they burned out in 6 months. Anyone have any suggestion for a rugged tube that is still punchy and doesnt sound like mud

JimmyM · #2 10-05-2011, 07:25 AM

If you are cranking the V4b into the red to get its wonderful distortion, then any tubes you use are going to burn out quicker than if you keep it clean. I'm assuming you're cranking it...?

jerkass9879 · #3 10-05-2011, 07:46 AM

I never go past 11/12. The head gets setup once a year. Recapped about 8 months ago when the last tubes were put in.

JimmyM · #4 10-05-2011, 07:54 AM

OK, then maybe you should consider NOS tubes like RCA, GE, Sylvania, JAN Philips, etc. They cost a little more, but not prohibitively more except for maybe power tubes or the most expensive of the NOS tubes like Mullards, Telefunkens, or RCA black plates.

arthur31686 · #5 10-05-2011, 08:20 AM

I've been cranking mine almost every time I use it in a band setting unless its at my blues gig. No idea when the tubes will need to be replaced. Sounds amazing though.

solodb · #6 10-05-2011, 09:15 AM

I have an early 70's V4B and it came with old JAN Philips 7027A's. They are the best for this amp , followed by RCA, Sylvania, Magnavox and other NOS American made brands.Sometimes you can find re-branded 7027A NOS tubes like MacIntosh, Groove Tubes or Wurlitzer that are actually made by the older American tube manufacturers. I have not been impressed by the JJ's, or Sovteks as they fail prematurely. The other big thing with this amp is keep it professionally maintained by somebody that really has experience with the Ampeg circuit.

beans-on-toast · #7 10-05-2011, 09:48 AM

+1 for NOS tubes.

As a precaution, you should have your tech check the plate and screen voltages on your power tubes against the readings that are on the schematic. The plate should be around 540 VDC and the screen 530 VDC. If the readings are higher, it is best to check the data sheets of the tubes that are being installed and see if they can take those voltages.

gerryjazzman · #8 10-05-2011, 10:21 AM

One other thing (and a tech would need to check this), is the output tube bias. If the bias voltage is too low, the output tubes will run hot and shorten their lives. Since the bias is not adjustable on the V4/V4B, any change in the value of a resistor in the bias network or a leaky bias filter cap could lower the bias voltage. I would have this checked before just replacing the tubes.

I installed a pair of bias pots and some jacks to measure the bias voltage and sensing resistors in the output tube cathode circuits so I could measure not only the bias voltages but the bias currents as well on my V4 (rescued from a beat up VT22 years ago). I'm running 6550's now, but this let's me run whatever I want and I can adjust the bias accordingly. I know. Should not have done this to a classic amp, but I wasn't thinking of that way back then.

BogeyBass · #9 10-06-2011, 05:41 PM

JJ's use the JJ's tubes. Great tube notorious for surviving in older high voltage amps. the V4 at 560 volts aint pushing the 7027 past its max at 600volts.
But some older fender amps pushed 6L6 beyond the max limit, like the bassman 135 or super reverbs. My point is, the best tubes to use in those tube cookers has been JJ's. Most other brands wont last long and the JJ's have been the ones to hold up. So thats why i would choose them. A matched pair of JJ 7027a tubes will go for 35 to 45$. About the only other easy to find 7027 will be the Sovtec. I have not had much luck with sovtec, i would only buy them if they were cheaper. you can hunt down old SED stock, but why...waste of time

No need to hunt down NOS tubes, spend a ton of money and then blow them too.

+1 for having a tech check the amp. Old silver caps dry out, high current resistors start to drift in value. Sometimes things are just worth the money, to me a V4B is worth it. at least check/replace
the bias caps and resistors. would be cheap to replace them to have a sturdy bias voltage.

Also the 470 ohm 5 watt resistor that supplys power to all the screens gets alot of abuse, likewise with all the 2 watt screens resistors and plate resistors in the power section. Depends on who is doing the work and your budget, you could just shotgun the whole thing and replace all the screen and plate resistors, the main caps and the bias caps. Ampeg/ Magnavox runs the screens to hot in my opinion at 530 volts, bring that down to 450 / 470 would be better.

still higher then what RCA recommends with a 560 plate which would be 400 volts on the screens. Ampeg and many others run the screen hot for more power. 530 is just a bit over the max value which is 500. just feel 450 to 470 would add more life to the tube. you can abuse the plates not the screens, Ampeg/Magnavox and Marshall all seem to have a hard time understanding this. blah blah blah ok i'll shut up now. JJ's get em

johnk_10 · #10 10-06-2011, 06:11 PM

my favorite tubes in my V4's and V4B's are NOS philips 7581A's. whenever replacing tubes in a V4 (as mentioned above) check their bias to see how hot or cold they're running. you can either add a trim pot to make it adjustable (mod it), or change a bias resistor to get the specific set of tubes that you're running to pull the correct current.