ATTN: What should I use in my vintage SVT?

I'm personally a fan of JJ tubes from Bob @ Eurotubes, they sound good, are not expensive and Bob's service is excellent. If'n you tell him what you're looking for he'll try to help match a set of tubes to get what you're after.

 

I'd let the shop technician tell me if I need new tubes!

 

I think you should let me use...your vintage svt.

 

Well, the ORIGINAL SVT used those 6146B, but that got changed relatively early.

The replacement was the 6550, and there was a conversion modification for the original ones. I've done a couple of the conversions myself, a long time ago.

I don't remember the details, but IIRC there is some re-wiring, the plate cap wires are taken out, etc. It's kind of a one-way street, in that after conversion, you can't use 6146 unless you un-do everything and put back the plate cap connectors etc.

So, you won't be needing any 6146 IF it currently has the KT88s.......... And I don't think there is any reason to go back to "original" 6146B tubes even if that's what it came with.

 

Yup.....you're right on everything. The 6146 was phased out by around late '70. My '71 had a tube chart on the inside with both tube types listed! I personally think the 6146 is a better SOUNDING tube, but they tend to not hold up under the rigors of gigging. I had my '69 converted years ago, and it ran great with 6550's. I've never been a fan of KT-88 in SVT's though. I think you lose some of the "Ampeg" when you get away from 6550.
Just my 2 cents!
Corey

 

Unless this is an original blue line (script on the front panel), that head never had those tubes. If it is fitted with the KT-88's, you wont want those regardless of what was original.

From what came highly reccomended to me by a very "in the know" source, Sovtek KT-88's, or Tung-Sol 6550's are a great match for the SVT's. Stay away from the svetlanas for these.

If you do a search, you will find the threads I posed a bit back where I got some great advice as well.

PS, make sure your tech checks all the solder connections, and it is probably due for a new set of caps as well. Check out www.fliptops.net for tons of goodies for these....I have spent a ton of time and dough there!

 

I have to isagree with your source. I've had nothing but problems with Sovtek/Tung Sol in Ampegs. The Winged C (former Svetlana) andd J.J. are far more durable and handle the voltages better, IMO.
Also, don't just have any tech work on it. MAKE SURE that he knows SVT's. They are a different beast than most other amps. Most failures I've had or seen have been from an "expert" that should have stuck to tape decks.
Trust me! I've owned more than 2 dozen SVT's in my life(personally), and sold many more through retail outlets. It's all I used for almost 20 years.
Corey

 

Ive got Svetlana 6550's in the power section of my SVT-II, nothing wrong with them i dont think, when i change them im going to get JJ KT-88's, either that or try and find some Philips ECG (Sylvenia) 6550A's, which were the tubes in it when i got it

 

Dude, you have a black line head which I believe, NEVER used those tubes but rather came with 6550's.

Also, 6550's and KT-88's are basically the same tube.

 

To further clarify, the 6146 tubes were only used in 69, which was a blue line model (yours isn't).

There are many rumors as to why the 6146 tube was used to begin with, a popular one being that at the time RCA had a bulk of them, and made magnavox (Ampeg) a heck of a deal on them to get rid of them.

I've also found that there is little to no tone difference betwen that tube and a 6550, except that it breaks up slightly sooner, and is a bit underpowered.

The mod to/from 6500/6146 is also supposed to be a techs nightmare in an SVT. Since there is nothing original about these inferior tubes in your head, I see no point whatsoever in changing it over to those.

 

Actually, the 6146 was used into part of '70 as well. As I stated in an earlier post, my '71 had the tube chart still in it that showed 6146/6550. That would mean it was a transition era model.
As for the 6146 being underpowered, most SVT's with HEALTHY 6146 will exceed 300 watts RMS. Most with HEALTHY 6550 will only get to 275 or so with a tail-wind. The 6550 has more attack, but the 6146 is smooth and round.
Ampeg used lots of whacko tubes because alot of the basic designs were straight out of the RCA Tube Receiving Manual.
Funny how most "Ampeg" branded tubes were RCA? Huh?
Corey

 

Oh yeah....I forgot to mention, my first 6146 SVT had black, square cornered graphics. DON'T go by the Ampeg Book! I've found all kinds of errors in there.
Corey

 

So does my 76 model, it means dick. There is a ton of conflicting info available, but to the best of my research, the 6146's were only used in the 69's. Regardless, the blue lines were made through 72, with the blacks appearing around that same time. That amp never came with anything but 6550's most likely....

However, I can't explain your black line with them, maybe psycho will come along and set us all straight soon.

 

Your first LABELED 6146, or first tubed?

 

I have a 6146B head. I believe its a 70. It has a painted chassis, and some internal parts from 12-69. it's a blue line.

Anyways, I agree with Tim, I didn't notice a huge difference between RCA 6146 and the 6550's that replaced them, and the tech did make it out to be a headache to convert it.

I've thought of putting it back to increase its value, but as a players amp the 6550's make sense.

 

No argument about JJ's being good, but I have over 100 Svetlana 6550C's that absolutely will NOT work in an SVT without modifying the bias supply because they run too hot and don't put out their rated power. These are all "Pre-SED" so there's no chance they're Reflektor tubes.

IME, I've found Sovtek to be superior tubes IF you get through someone who carefully pre-screens them. I have one sextet of Sovtek KT88's I got from Hong Kong (I THINK from the same store westland posted pictures of) and the rest have all come from Ned Carlson at Triode Electronics. I have had NO problems with them or the the sextet of Sovtek 6550WD's that came stock in my Eden VT300.

I have a 73 that has 6146's on the tube chart. Magnavox used old parts stock whenever they found it.

A 6146 and a 6550 are for all intents and purposes, the same tube with a differing pinout. SOME old 6550's have a higher screen voltage rating. However, ALL modern 6550's are based on GE's 6550A and higher powered than a 6146 with better voltage handling on the plate and screen grid. There is NO point of changing an already 6550 equipped SVT to 6146's. It IS a pain and you WILL be lowering the amount of power the amp puts out.

They did that with the V4, V4B, B15N and B15S because RCA was trying to move 7027A's and Ampeg fell for it. RCA never made a 6146; they were all GE rebrands.

Actually most "Ampeg" and later "Magnavox" branded tubes were Sylvania. RCA quit making tubes in the late 60's entirely. ALL "RCA" branded tubes from that period on were rebrands from other manufacturers.