Vacuum tube ! And Warnings

To all out there who have Vacuum tube Amplifiers .
my friend just bought his first tube amp , it came with EL34 power tubes he wanted to get a bit more punch . He ordered on EBay  6550s I told him I would assist in fine tuning the bias.
he plugged them in we turned it on and a huge transient goes through one of the speakers and a surge through one tube . I shut it down waited 5 minutes then turn it on bias has a built in meter ,I checked they were over 90 +milliamperes maxed the meter. should be around 50. I removed them , he is sending back.the story here is many Ebay sellers don’t even test them they just get them from Russia and state as a match quad ,and runin for 24 hours . Never buy from anyone that doesnot  personally check them .
viva tubes, and upscale Audio are good , Jim mc Shane is good.
for vintage tubes, Brent Jesse recording, and Vintage tube services   I recommend. 
Perhaps a dumb question but can the amp run 6550s?
Just because the tube fits the socket, doesn't mean the amp runs the tube. 

Bias is set on the amp. Changing tubes doesn't change the bias. 50 to 90 is nothing in terms of harm, certainly nothing to cause such a show as this. 

Clearly you have other problems. The lack of relevant details and providing irrelevant info being a bit of a clue as to the biggest one.
A 6550 tube is not a direct substitute for an EL34 tube.

Hopefully the amp was not damaged by installing the 6550 tubes in the amp.

El34 data sheet

6550 data sheet

Prudent step one, before inserting new tubes(when possible): turn the bias to zero.     That's after one has ascertained amp/tube compatibility.
The amp in question can take el34- kt 150s
It is a custom canary amp
I was just making a point nothing more
i have been using tubes for over 40 years 
and owned a Audio store I know how to bias tubes. My point was a lot of eBay sellers don’t even check the tubes they just 
go by what the mfg state I later checked
with a textronics tester 2 tubes were at over 100 most ma meters go to under 90.
that is why you buy tubes that should be within range under 70 ma for sure
6550-kt88 50-60ma is the norm
I would never buy tubes off eBay. That was the first mistake.  
I tend to disagree as there are some long term excellent dealers on eBay. The trick is finding them, that’s all. I bought a whole bunch of tubes on eBay about 6-8 years ago , everything from Chrome Domes to Badboys to WWII Tung Sols, always had great results. 
"I would never buy tubes off eBay. That was the first mistake."

In the last 12 months, I've purchased around $1k worth of NOS tubes from sellers on Ebay. Zero problems. Years ago, when I had an amp that used 6C33 tubes, I purchased at least $500 worth from sellers in Russia and the Ukraine. Zero problems. I always purchased from sellers that had 100% positive feedback.
I have had 2 bad experiences on eBay. Not for tubes, but for other audio equipment.  In one case, it was an Acrolink cable that never materialized after waiting 9 months.  The other was on an amp that arrived broken (not from shipping) and had a very hard time getting a refund.  Too many amateurs selling on eBay so now I avoid at all costs. 
agree with Stereo5 on why would anybody buy tubes off of Ebay ?   

if you knew your friend was going to get tubes, why not suggest getting them from a tube dealer that would have the tubes matched / tested ???

there was another thread recently about someone getting tubes from Ebay and they are all shocked that they were junk.    duh.....
“Not for tubes.” There it is! 🤗
my friend bought them ,and told me after he had them in his possession.
i told him ,he is sending them back 
pronto tommorow ,it was a very valuable lesson learned and luckily no damage .
Saying that every tube seller on ebay is bad is a bit of a head scratcher. I bought two matched quads of KT120’s back in October from ebay for my Rogue Audio monoblocks and no issues whatsoever.

I just biased my amps today and the tubes in one amp had not drifted at all, and in the other amp, a couple of tubes were just a hair off. That particular seller has about 19000 transactions and 100% feedback. I would keep an eye on those numbers when considering making ANY purchase from ebay.

I’ve bought tubes from Brent Jessee and a couple have had had issues. That doesn’t make him a bad seller. He arranged to get me new ones pronto and was super helpful when I had questions about the best tubes for my gear, listening preferences, and budget. I recommend him highly.

I’ve also had issues with Sophia Electric tubes. Same thing, they got me new ones quickly and were easy to deal with. I’d also recommend them.

I don’t know how the other seller would have responded if I had problems, since I haven’t.

Exercise common sense and good judgment when buying from ebay, the same as you should when making any online purchase. Don’t lump all sellers into one bucket because of a couple of bad ones.

I am baffled here you put tubes in an amp that can't use 6550s? You said EL34-KT150 does that include 6550s? If not its not the fault of the tubes wherever they came from it's user error.
Some Quicksilver amps can use a number of tubes.... the bias pot has enough range but like rodman said turn the bias completely counter clockwise first then slowly up to bias spec.   My QS can use EL34, 6L6, 6550, Kt66, KT77, KT88, and some others.   
hello Jond  the amp can take anything from El-34,  KT-88-6550 kt120,kt150s
+1 Big_Greg. Very well said.

I've made a few tube purchases on eBay, with 100% perfect results as verified both sonically and on my Hickok tube tester. Of course the purchases were made after thoroughly checking out the seller's feedback/feedback left for others/other items for sale, etc., to get an idea of what kind of person I would be dealing with.

On the other hand, I've had issues with tubes purchased from both of the well known sources Big_Greg mentioned. Which ultimately were resolved reasonably well, although I'm not sure that would have happened if I didn't have a tube tester to help diagnose the problems.

-- Al
I had problems with two NOS Mullard CV4003 tubes.  One went microphonic after a week and the other after six weeks.  I paid almost $100.00 each at the time.  Lucky for me Kevin Deal backs up his tubes and I got replacements that lasted a long time.  The ones I bought were Upscales highest grade.  I guess any 40+ year old tube can have problems. 

03-08-2020 6:14pm
hello Jond the amp can take anything from El-34, KT-88-6550 kt120,kt150s

Is this the same amp you are selling here?
It’s hit or miss. Recently bought a nos Siemens 6922 off eBay. Got it and checked it out on my Hickok. Tested at 1500 which is really bad. It doesn’t sound bad after I compared it to a newer gold lion but I was disappointed. That tube was 100$. Tube selling is big money and many of these sellers don’t test them properly. 
Every few months there is a thread titled "Where Do Buy Tubes" or "Good Tube Vendors".  Good Reading.
Call me confused.....

audioman58 OP said:
To all out there who have Vacuum tube Amplifiers .
my friend just bought his first tube amp , it came with EL34 power tubes he wanted to get a bit more punch . He ordered on EBay 6550s I told him I would assist in fine tuning the bias.

audioman58 OP1,581 posts


It is a custom canary amp

ozzy62822 posts

audioman58 OP Said:

03-08-2020 5:14pm
hello Jond the amp can take anything from El-34, KT-88-6550 kt120,kt150s

Is this the same amp you are selling here?

KT150 tube datasheet
I've bought a lot of vacuum tubes from many EBay sellers.  I guess I've been really lucky. 
That being said, My favorite seller is LeedsRadio on Etsy. I can recommend them without hesitation.

Since I don't have any tube testing equipment, I'll just have to continue to rely on good luck and careful examination of buyer feedback.
I've had great luck from Ebay tube sellers, including one guy in the next town who delivered the tubes himself to my mailbox...twice...
A couple of years ago I bought a PS Audio BK preamp (the latest one) from a seller here on Audiogon. He replaced the stock tubes with two tubes he bought from The Tube Monger. The seller claimed that the preamp sounded MUCH better with the new tubes, He also provided the original factory tubes. The distortion coming out of the preamp was so bad I couldn't get an output to my computer to produce an undistorted wave file! I sent the tubes to PS Audio who checked them and told me to throw them out. I reinstalled the factory tubes and the preamp performed perfectly. I'd say that the seller was a "tube roller wannabe". If the preamp had tubes that PS Audio felt were excellent and reviewers agreed, why mess with perfection. Joe
Plus for Brent Jesse.

I bought, didn't like the sound of a brand I had selected, he allowed me to burn them in, then decide, then return them, sent me my alternate choice (I know I like their sound, had some in stock), which cost less, and refunded the difference to me.

A true gentleman.
I just looked over Canary's listing on their EL34,,,does anyone see where it says the EL34's can be swapped  out?
The amp looks to me like a  EL34 amp and no other tube allowed.

I just can not lay the blame on the tube quality.
mozartfan145 posts


I just looked over Canary’s listing on their EL34,,,does anyone see where it says the EL34’s can be swapped out?
The amp looks to me like a EL34 amp and no other tube allowed.

I just can not lay the blame on the tube quality.

I looked last night and couldn’t find one built by Canary that supported El34 as well as 6550 tubes either. Maybe the OP will chime in and post the model number and a Web Link.

Black Ice Audio makes a couple of amps where both EL34 and 6550 tubes can be used. The Fusion F-22 and the Fusion F-35

One thing for sure if the amp came with EL34 tubes and the owner pulled the EL34 and installed 6550 tubes he should have first cut back the bias pot setting before powering up the amp. If he did not, he probably caused damage to the 6550 tubes. Good thing the guy didn’t buy the 6550 tubes from UA. He could forget about getting a refund.

Here is a good video on the subject.

Direct tube substitutions.


I would never buy tubes off eBay. That was the first mistake.  

I've bought all kinds of Valves from eBay. A good visual, and a way to check is the only way a valve goes in my units, ANYWAY. I don't care who sold it... It has to get to you somehow, THAT alone is a reason to check it.. Normally, no problem, but there is that 20 foot slide across the the UPS, FEDX, USPS, trailer floor, into the brake lining being transported on the same trailer.. That's also had lawnmowers, condoms, and laddies brasseres (some men too) all on the same cargo run...SQUASH comes to mind....I've had a bad one or two, all signal valves though no power valves...just cheap, burn out before you could blink an eye stuff, with power valves.. 6L6 stuff usually.. Solvex is pretty good for the most part..
I like um...I just don't trust um....

You know I though about what you did. That can't work their wired different, I don't think you can swap that valve. I'm not an EL34 guy.
Where's the bass?? But really, I don't think it's interchangeable.. Two different animals all together.. A guy told he could do it with VTL, from KT90, to EL34, with a flip of a switch, and of course a rebios (maybe he had some type of auto bios). My VTLs no switch, 6550, Kt88 or 90s no EL34 for sure..They are wired different...No plug and play....

Yeah EL34's seem not same league  as 90/88's/6550's. Seems altogether dif design. Its like a  minature 90.

I know there are quite a  few audiogoners who havea  negative bias on buying tubes from ebay sellers.
I've bought quitea  few lately and have no issues. 
Nearly all test as seller states.
The reputable dealers prices are out my budget, ebay offers a  opportunity to purchase these fine NOS tubes. Test strong is OK with me. Sonics on a strong tube will be identical  with a  NOS.