|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
173.175.57.206
I have been out of the world of tube equipment for a while and recently got back in. And it is time to retube my new-to-me amplifier. So I have a few questions about matched pairs/quads etc.
There are a lot of vendors to chose from; Tube Depot, Tube Store, Amplified Parts, Larry Curley, and Moe Electronics just to name a few. All of them claim to do matching, which I have no reason to doubt, but none provide much detail to tell me who does the closer matching.
I have read articles on what is important so I get the basic idea but without any specifics from suppliers it does not mean much. Recently bought a matched pair and when I asked what the standard was I was told they had no idea but their supplier says they are matched; will not be using them again.
I am open to hearing who you use and what your experience has been.
Follow Ups:
+10 for Jim McShane. Read his sticky...
https://www.audioasylum.com/audio/tubes/messages/25/253369.html
especially #6
6. Other components besides the tubes themselves can make your matched tubes seem less well matched. Power tubes may be matched for transconductance, but it is imperative that if you need matched tubes that they are matched for current - some say plate current, I say CATHODE current. Why cathode current? Because between the cathode and ground of many (most?) power tubes you will find a resistor in the circuit - low value, 10 Ohms is common - and that resistor's purpose is to make it possible for you to measure the voltage across that resistor and use Ohm's Law to calculate the current. Measuring the current with an ammeter requires breaking into the circuit and inserting the current meter. But with a voltmeter we don't have to break into the circuit, we can measure the voltage across the resistor and know the current flow through it. For instance, if you read .5 volts across a 10 Ohm resistor you can compute the current flow by dividing the voltage by the resistance. .5 volts divided by 10 Ohms = .05 amps, 50 milliamps.
Don't forget about some of the eBay sellers who claim a matched pair of tubes are two that look alike. Yes this is meant to be light hearted but sadly true.
Contact McShane he is a great guy and will do a fine job for you.
Cal
i am afraid, matched in tube business means nothing but just one single plot-point on the tube´s graph and not completely compared an combined by indentic graphes.
so matched pairs, quads etc. mostly are every thing else than correctly "matched" and means marketing only. am i right?N.
Just smile - it confuses other people.
Edits: 07/19/20
Maybe that's what it means to you?
I spend a huge amount of time sorting out NOS stuff (yes the spread can be enormous).
To give you some idea, out of a box of 15 s/h 807s I got maybe 2/3 pairs.
Idem when I weeded my way through 25 NOS 5B254M (STC 807).
From the 25, 3 were DOA, making an internal arc/flash when started up.
Several were weak, several were uber-strong.
In the end I got 2 quads and a few pairs out of it, with the duds just going for decoration.
From my large boxes of 250+ NOS pentodes I get a spread of between 9m/a (well under spec) under true working conditions to 22m/a (well over spec).
As they degas, within a few minutes they stabilise, so you have to let them get warm.
In my dual QUAD pentode amp I match all 8 to within 6%.
It takes a lot of patience, because they do drift a little.
How do I do it?
I fit them in a fully working amplifier and check them one by one, inc a full power test to see if there is any change in SQ wave response or THD/IMD.
a smart technician told me, he matches power tubes in the amp they are destined for. so do i now - and that works great!
Just smile - it confuses other people.
Edits: 10/13/20
i am afraid, matched in tube business means nothing but just one single plot-point on the tube´s graph and not completely compared an combined by indentic graphes.
so matched pairs, quads etc. mostly are every thing else than correctly "matched" and means marketing only. am i right?
N.
Just smile - it confuses other people.
A reliable dealer labels the cardboard box with the measured values for gm and cathode current. Also, experienced dealers test the tubes under conditions resembling those found in working amps.
Factory matching by the current tube builders is, to be charitable, suspect. Competent dealers know which amps "like" tubes that bias either "hot" or "cold". A specific set of tubes may be well matched, but a poor choice for a given amp.
BTW, my go to guy, AA sponsor Jim McShane, is a big 3 Stooges fan. ;> )
Eli D.
Good info. I understand the concept of using the manufacture of the amp for the best matching, but my understanding is that they won't sell me tubes, and shipping round trip would be $800 and a three-month wait as they are starting back up from the COVID.
I may check out Amplified Parts as they use the Apex system which seems to be well thought out and provides plate current and transconductance.
You misunderstand me. Amp manufacturers overcharge for replacement tubes. :> ( Guys, like McShane, who truly know their business are who you go to for replacement tubes. Competent dealers know what works with specific amps and act accordingly.
Eli D.
"Amp manufacturers overcharge for replacement tubes."
Not all overcharge. I've found Manley's tube prices pretty reasonable. And Jim McShane does terrific work.
WW
"They were running on fumes, dazed and confused, in a high-powered automobile."
Does McShane's business have a name?
Yes, he does. He sponsors this board.
Link to Mr. McShane appears below.
Thanks, I will take a look
I'm working with him on putting an order together, and he's taking the time to look over a phono circuit for me and has made a few suggestions.
Jim goes above and beyond.
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: