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V4B tube conversion or leave?

M

markorbit

Apr 16, 2004
626
173
#1
Just picked up a 76-79 white rocker V4B and my initial thoughts on it were not as good as in the brochure. My Trace V4 has better grind and that's just by driving the preamp gain.

However, on closer inspection it seems there is no 12DW7 tube present (it was a 12AU7 in that slot) so I'm replacing the preamp tubes (Jan/Phillips/Amperex/Svetlana) in addition to having a cap job from Fliptops.

I read a review that said EL34's can sound real good in these units and I do seem to remember that EL34s had a sound I liked in old Marshalls. Power isn't an issue but growly tone is. I like warm, dry, punchy, grindy and musical non-harsh mids. The closest I have heard is an overdriven SVT.

What I want to know is... the power tubes are chinese Ruby 6l6GCs and I may be replacing those next. Should I consider converting to EL34s or stick with 7027/6L6s? Any recommendations?
 
#3
markorbit said:
Just picked up a 76-79 white rocker V4B and my initial thoughts on it were not as good as in the brochure. My Trace V4 has better grind and that's just by driving the preamp gain.

However, on closer inspection it seems there is no 12DW7 tube present (it was a 12AU7 in that slot) so I'm replacing the preamp tubes (Jan/Phillips/Amperex/Svetlana) in addition to having a cap job from Fliptops.

I read a review that said EL34's can sound real good in these units and I do seem to remember that EL34s had a sound I liked in old Marshalls. Power isn't an issue but growly tone is. I like warm, dry, punchy, grindy and musical non-harsh mids. The closest I have heard is an overdriven SVT.

What I want to know is... the power tubes are chinese Ruby 6l6GCs and I may be replacing those next. Should I consider converting to EL34s or stick with 7027/6L6s? Any recommendations?
Click to expand...

HI

EL34 heaters take 1,5A current and 6L6 or 7027 take 0,9 (900mA). The heater supply might overstress (burn) with EL34 or 6550 or KT88. If the heater coil can take 67% more stress, then you can do it. I don't recommend it. Check it with a good tech.

"It IS an SVT realistically"

Sorry, it is not near "an SVT". The power amp is essentially different (no high voltage cathode follower between PI an power tubes). The anodevoltage (B+) is under 550 V, SVT has nearly 700V. V4 has four 7027 -> power around 130W. SVT has six 6550-> 300W power.
The preamp is closer to SVT, but for example the "ultra low" is different. (in my oppinion not as good)
 
#4
While I cannot offer the technical expertise/explanation that okabass does I can say that the SVT and V4B do not sound the same.

More precisely, no matter what I do to a V4B I can't get it to sound like the SVT's channel 1. I can get the SVT's ch. 2 to sound close to the V4B though.

I know there's a saying: V4B is SVT's little brother and all that. I don't think it's true even after having my V4B converted to 6550.
 
#5
markorbit said:
Just picked up a 76-79 white rocker V4B ..
Click to expand...

I just bought the same amp and have similar questions. My V-4b has all the original tubes marked Magnavox. I was not happy with how this amp broke up at relatively low volume and I replaced the 2 12ax7 preamp tubes. This did help some.

Can I replace the 12dw7, 12au7, and 6k11 tubes without having the amp internally adjusted (biased)? Any suggestions to brand of tube?


Any/all recommendations welcome!
 
#6
MotorTed said:
Can I replace the 12dw7, 12au7, and 6k11 tubes without having the amp internally adjusted (biased)? Any suggestions to brand of tube?
Click to expand...

No biasing needed with preamp tubes so experiment away. Not too sure about the widespeard availability of the 6K11 but they do show up on ebay. I snagged 3 RCAs last week.

I was recommended Jan Phillips for the 12AX7 and Amperex for the 12AU7 but I find the difference between decent tubes to be very small. I don't think I could pass the bllidfold test although I did find the Jan Phillips to be more punchy and musically compressed.

I think.

Tried the V4B again today and at the Trace V4 still sounds much better. Hope the V4B improves with the service and parts. I find it a bit 'hard-sounding at the moment. I also can't quite work out whether I want to boost 300hz or cut 1kz!

Oh and you have the original tubes in there I think. Nice one.
 
#7
markorbit said:
Just picked up a 76-79 white rocker V4B and my initial thoughts on it were not as good as in the brochure. My Trace V4 has better grind and that's just by driving the preamp gain.

However, on closer inspection it seems there is no 12DW7 tube present (it was a 12AU7 in that slot) so I'm replacing the preamp tubes (Jan/Phillips/Amperex/Svetlana) in addition to having a cap job from Fliptops.
Click to expand...

A 12AU7 will make significant difference in the preamp and the overall response of the amp. The high gain half of the 12DW is not present to provide necessary voltage gain for the preamp and you're not going to get grind as easily.

I read a review that said EL34's can sound real good in these units and I do seem to remember that EL34s had a sound I liked in old Marshalls. Power isn't an issue but growly tone is. I like warm, dry, punchy, grindy and musical non-harsh mids.
Click to expand...

...then you definitely do NOT want EL34's. Their defining sound IS their strong midrange, specifically the upper mids. They're only good if you're not worried about losing bottom and like an aggressive rock tone.

What I want to know is... the power tubes are chinese Ruby 6l6GCs and I may be replacing those next. Should I consider converting to EL34s or stick with 7027/6L6s? Any recommendations?
Click to expand...

I say stick with 6L6GC's.
 
#9
Psycho Bass Guy said:
...then you definitely do NOT want EL34's. Their defining sound IS their strong midrange, specifically the upper mids. They're only good if you're not worried about losing bottom and like an aggressive rock tone. I say stick with 6L6GC's.
Click to expand...

Yeah, I'm heading that way. I do still like the midrange to have some teeth but without the harshness of some amps. I would say right now it lacks some low mid/high bass. I can rattle the room by turning the bass up but that seems to be lower than what I'm looking for and I need more meat on the sound.

12DW7 should arrive any day. Then I may look into replacing the Rubys.
 
#10
Before you do anything to modify it, get it restored to it's best working condition stock, ie good tubes, new PS caps etc and then compare it to other amps and see how you like it.
 
#11
KojakCurtis said:
Svetlana (winged C) 6L6's broke up way too early, so I had JJ Tesla 7027A's installed in my 1974 V4B and it sounds great. I don't think 6L6's are a good choice for the tone I think your looking for.
Click to expand...

I was thinking of going with the 7027a replacement. The 4 I have now glow blue when pushed hard-evenly though. The Standby light also seems to pulsate slightly, similar to a florescent light bulb. Are there bias pots in the V-4b? Would they need to be installed or would a matched set of 7027a's be plug and play?
 
#12
KojakCurtis said:
Svetlana (winged C) 6L6's broke up way too early, so I had JJ Tesla 7027A's installed in my 1974 V4B and it sounds great. I don't think 6L6's are a good choice for the tone I think your looking for.
Click to expand...

There is NO difference between a 7027A and a 6L6GC in an Ampeg V4. ALL output tubes MUST be properly biased before you can make any accurate judgements as to how they 'sound.'
 
#14
Tubes biased too hot can glow blue and the extra current draw from too hot operation could conceivably draw down the power supply and cause the pulse you see in the standby light. I'd check your fuse and make sure it's the right value. Given the amp's behavior, the mains fuse should be blowing before you start seeing those other symptoms if it is bias related, and you possibly have too high a fuse in there which could lead to some REAL trouble down the road.
 
#15
MotorTed said:
Is the blue glow and pulsating standby light an indication of anything wrong?
Click to expand...

HI

Blue glow is ok.

http://members.aol.com/larrysb/blue_glow.html

Which type is the st. by light? Led? incandesent lamp ?
Usually the st.by light is just an indicator: if it breaks, amp still works.

Off cause, if the amp has some protection circuit, and the st. by lamp is also its indicator, then check amp manual or contact your tech. Some lamp types can flicker a bit by nature.
 
#17
Psycho Bass Guy said:
Flourescence CAN be OK, but if the amp is acting and sounding funny, I still say take a look at bias. My V4 did exactly the same thing when I bought it. Guess what the problem was?
Click to expand...

HI

I agree with the bias matter. It is very important, that it's correctly adjusted.
You amp might have had that blue glow at the same time as the bias trouble, but according to:

"Sylvania Engineering Data Service", vol. 1, pg 23 (1960?):

BLUE GLOWS

Blue Glows are _not tube detriments_ per se. They are, however, suspects in the eyes of many receiving tube users for lack of a full understanding of their origins. There are several types of Blue Glow which can be described as follows:

FLUORESCENCE-this type of glow is usually violet in color and most noticeable around the inside surface of the glass bulb. It is most pronounced on power tubes and is the product of electron bombardment of the glass taking place within the tube. It generally has no adverse affect upon receiver performance, and in fact, tubes displaying this phenomenon are particularily good with respect to gas content."
 
#18
Just ordered some JJ 7027s. With those, the caps, all the correct preamp tubes, we'll see how it sounds. One thing I do notice right now is that it really compresses the signal, makes the bass sound very even across the board, even at low volume. Quite snappy.
 
#19
Psycho Bass Guy said:
There is NO difference between a 7027A and a 6L6GC in an Ampeg V4. ALL output tubes MUST be properly biased before you can make any accurate judgements as to how they 'sound.'
Click to expand...


I appreciate all the information given. I have more questions now.:hiding: I would agree that the 7027a and a 6l6GC are the same based upon all the reading I've done recently. It was my perception that my 76-79 V-4b with original 7027a tubes was louder than a new V-4bh I tried which has 6l6 tubes. I didn't try both amps together and there was a few months between(both were tried through a Ampeg 6 x 10).
Is my perception of the louder vintage amp flawed or is there more of a difference to it than power tubes?
 

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