Power Tube Saturation

[DrewV]

Hi All,
I have a few questions about tubes, but first, some history...Lately I've been doing some repair work on a 1978 Ampeg V4 head.This amp uses 7027 power tubes. While researching the V4 I learned that the 7027's could be replaced with 6L6 GC's or equivalent. Digging out my small collection of various "good" 6L6's and 5881's (GC & WXT), I began subbing out tube pairs, a duet at a time on the inside sockets. If you have never heard this amp, it is not only LOUD, but setting the volume (no master volume on this one) from 3/4 to full open yields the most incredible sounding power tube saturation I have ever heard! I can barely get close to it with my Mark IIC clean channel and master wide open. Running the channel 2 master wide open with the Lead Drive dialed in low is a little closer, but tonally not that close. Even running the old stock 7027's produces "that sound". Now to my questions. 1) Is it possible to alter a Mark IIC with different tubes or other passive components to get that luscious power tube saturation? 2) Is it possible to substitute the 6L6's in the Boogie with 7027's? and 3) Would biasing the amp hotter cause the power tubes to reach a deeper level of saturation?
Thanks
DrewV

 

[acorkos]

IMO, there's more than just power tube saturation going on in your V4 that's contributing to the sound you're hearing. a 6k11 preamp tube for one, and a pretty sophisticated midrange circuit....it would be difficult (and impractical) to modify a Mark IIC to have the same preamp elements to give you the sound of your V4. IMO, the V4 has a unique (and incredible) sound (and it's loud!). I say enjoy the V4 as is, and enjoy the IIC as is...as you discovered, the higher you can raise your master volume on your IIC, the more power tube saturation comes into play...but wear your earplugs!.

Hotter power tube biasing would allow the power tubes to be pushed into saturation at lower volume control settings, but your clean tones may suffer.

I don't think you'd notice a lot of difference with 7027's in your IIC....they are just a studlier version of a 6L6. The JJ 6L6GC's can take upwards of 500V on the plates....they are a direct drop in replacement for the 7027 tube (JJ also makes new production 7027's to keep the nit-pickers happy, but they are virtually, if not exactly, the same tube).

 

[stokes]

Another consideration with power tube saturation in the IIC is that a lot distortion is generated in the preamp itself.If you try to saturate the power tubes too much your distortion can get pretty ratty sounding,particularly in the lead mode.I do like power tube distortion,and in my IIC+ I have some NOS 7027A's that too me offset that "rattiness" better than the 6L6GC's biased hotter than the Mesa settings.Bear in mind that you would need to wire the IIC for adjustable bias first.That V4 is pretty clean in the pre as compared to the Mesa,and is mainly designed for max headroom,that is why you get earsplitting volume before the power section saturates.The 7027A's dont break up as quick as the 6L6GC,so even tho a GC can be used in the V4,they will saturate sooner than the 7027A,so that would be a better choice if you are looking for power tube distortion.I wouldnt recommend using a "true" 5881 in that V4,it may not survive too long.

 

[herrball]

OK, this is a real problem here. After reading the posts on the Ampeg V4 I want to pick one up!!! ;-) I actually had one back in 1980 ( high school) prior to a Marshall and Boogie. But I digress........

If the V4 has 4 power tubes, couldn't you just yank the outer 2 tubes to reduce the volume? Couple that with an iso box for recording and away you go........ I certainly would like to know if it works in case I find a decent price on a V4. I remember it had great rocker switches for changing midrange poinjs in the EQ and I could get great Santana tones/sustain with my now lost, 1977 Ibanez Les Paul copy.

Now to eBay!!!

 

[stokes]

OK, this is a real problem here. After reading the posts on the Ampeg V4 I want to pick one up!!! ;-) I actually had one back in 1980 ( high school) prior to a Marshall and Boogie. But I digress........

If the V4 has 4 power tubes, couldn't you just yank the outer 2 tubes to reduce the volume? Couple that with an iso box for recording and away you go........ I certainly would like to know if it works in case I find a decent price on a V4. I remember it had great rocker switches for changing midrange poinjs in the EQ and I could get great Santana tones/sustain with my now lost, 1977 Ibanez Les Paul copy.

Now to eBay!!!

Yes,but be sure to change the speaker load to match the 2 output tubes.It would be advisable to check the bias also,it can change some when pulling two tubes.As for the new load,if the 4 tubes were meant to go into a 4ohm load,two tubes would want to see 8ohms.