Vintage Ampeg tube changes

[Tomm Williams]

A few months back I posted about picking up a 1960 Ampeg Rhapsody. Tonight I was notified by Ben Fargen that he competed the repairs on it which included a new PT, conversion from the original EL37's and a whole lot of of other needed replacement parts and maintenance.

He stated in his email that due to the type of PT he installed, I could change between 6l6, 6v6 or EL34 power tubes. And as its cathode based, no biasing needed.

So I'm wondering if there are any general characteristics I could expect from each type of tube? Just about every amp I own has 6l6's so something different is appealing. This amp still retains its vintage Jensens as well.

He said it was probably the most unusual amp he'd ever seen so I can't wait to finally pick it up this weekend.

[WRGKMC]

Guitarists tend to count on how the sound feels when playing just as much as they do how it sounds. I suspect its because they feel the string vibration from the instrument directly and match how the sound from the speakers impact them to get a balance between the two. A flubby sound from an amp for example can put a drag on your playing as you wait for it to catch up with you. An overly bright piercing sound may not be compressed enough to give you a comfortable string attack.

 

As far as the difference in power tubes, if you were to leave the tone controls set the same there probably wont be that great a difference, but if you are the type who manipulates the EQ and gain to get the best feel - tweak till you find the amps sweet spot, you should find the tubes quite different. I find the 6L6 tubes as being great for obtaining big plush tones. The EL34's have a tighter bottom end and a faster response in the upper mids which affects the string picking and brings that up front.

 

You wind up having a sweet spot in a different place. Single notes are crisp and clear, excellent for playing leads without the latency 6L6 tubes have. Its something you simply have to experience. Chances are you'll have to push the amp a bit harder to get those sweet tones, and it does take time getting used to it but it can open up a whole range of tones you've never realized existed.

 

I cant say how well that Ampeg will do getting the two distinctly different sets of tones. The Ampeg's I've owned do some unusual things with the midrange tone stack by placing it later in the chain and adding an additional gain stage. As a stock amp I always recognized it as being and amp that's sat between a Marshall and a Fender being able to hit either extreme but sitting between the two in tone when dialed for its strongest tones. That was using the original 7027A power tubes those silver faced Ampeg's used.

 

Ampeg has changed its circuits and tube types many times over the years. The amps often keep their unique signature tone because much of it is based on their tone stack. Its only when they are driven hard into saturation when you begin to notice the differences with power tubes. I suspect that will be your experience too. Ampeg has reissued amps like the V4 using 6L6 tubes and from what I've heard sound very similar to the older 7027A tubes. If anything I think the amp will have stronger upper mids and less flub with the EL34's. You'll have to be the judge on that however. The chances of you coming across someone else with that same amp, no less the same modifications isn't going to be very likely so all other can do is give you some general assumptions like I have.

 

I do suggest you be open to the option of using different speakers with the EL34's. They tend to favor British voiced speakers to get a better tone balance and drive. You may wind up missing out on some important tones those tubes can produce using the Jensen frequency spectrum and masking some of the tone and saturation those higher power tubes can produce. the power tubes, transformer and speakers are all equally important in getting the most from the power amp. Any one of them can bottleneck your sound if they aren't capable of working together well.