I wonder if I could build a test jig that allowed me to take two unmatched tubes and burn the higher one down to the lower specs.
Just playing devil's advocate. What are you trying to match? DC parameters, AC parameters? Isn't this akin to turning one strong tube and one weak tube into two weak tubes?
I wonder if I could build a test jig that allowed me to take two unmatched tubes and burn the higher one down to the lower specs.
Just playing devil's advocate. What are you trying to match? DC parameters, AC parameters? Isn't this akin to turning one strong tube and one weak tube into two weak tubes?
Yes - except even the lower tube would have to test strong. I'm also not thinking of using this for huge differences. most likely if the tubes are off 20% pull them closer to 5% or 3%. It's really just to save mismatched NOS / Pulled Vintage tubes / or getting the most out of buying bulk tubes.
I'm guessing since then are going to be all over the place it would need to be adjustable both for DC and AC power so you can control the burn. As well as all other parameters.
it's less about making the tubes work for personal reasons ( I could easily convert the bias to dual) It's more about making them matched sets for amps that I would hate to see bastardized.
mis matched tubes can work in certain amps they sound better in others.
the problem is one tube is forced to run cold or burn hot.
or both are compromised and then who knows
it also depends on the style of music and which notes as to how the sine wave is recreated and procieved to your ear.
Correct it'll have to able to adjust for both transconductance and idle current. I never said i had a way or and answer just an idea.
I'm going to experiment a bit with the amplitrex and see what i can do. It allows me to write the test sequence. I'll see if i can't nibble away at a tube and close the gap.
If you are talking about thoriated tungsten based tube filaments there are actually techniques that can be used to rejuvinate or unpoison the cathode. These techniques ruin typical indirectly heated tubes I think though.. Still interesting, especially if you can find an old set of 300B's for cheap.
I can't say enough good things about the Amplitrex.
I have it hooked up to a desktop and printer along with two brother label printers, one for the tube sockets with octal bases, the other to print labels for boxes. I also have a laptop loaded with the software for field repairs. Though the AT1000 functions in a stand alone mode on it's own, so the laptop is not required for basic good /bad /matching tests.
It's a very useful piece of equipment.
I'm not sure how cost effective it would be to reverse engineer, it's got several computer programmed chips so unless you have a way of programming them (correctly) it's a mute point.
Cliff Schecht wrote:If you are talking about thoriated tungsten based tube filaments there are actually techniques that can be used to rejuvinate or unpoison the cathode. These techniques ruin typical indirectly heated tubes I think though.. Still interesting, especially if you can find an old set of 300B's for cheap.
My dad and I considered worrking on a tube tester that was a matrix of 9x9 relays connecting to up to a 9 pin socket (higher pin sockets need more relays). The whole thing would be controlled by a microprocessor and could do all sorts of automated testing and such. Projects like this don't manifest quickly or easily though and with me always being at least 6 hours away, the idea sorta died away. Still, this seemed like a relatively efficient way to test different tube types quickly. You could even implement features like automatic pinout detection and perhaps have a small list of compatible devices to select from making it easier to change tube types.
selloutrr wrote:mis matched tubes can work in certain amps they sound better in others.
the problem is one tube is forced to run cold or burn hot.
or both are compromised and then who knows
it also depends on the style of music and which notes as to how the sine wave is recreated and procieved to your ear...
Good points to consider. Do we believe that there is only "one" golden sweet spot that brings everything we want out of a tube? It occurs to me that there can be merit in running them a little hot or running them a little cold, depending on what you are after. I know that we'll get disaster if we take that to extremes but is it possible to get a little bit of the good out of both if they are mismatched just a bit? I am curious if this explains why a mismatched set can sound good to my ears?
cliff-
what you are describing is basically a stripped down version of what the amplitrex does. I have hundreds of tubes pre loaded into the system so all i have to do is type the model and the test specs come up then decide which tests i want to run and how i want it to be configured and press the start the button. like toast a few minutes later it's done. other then that I can pick the heater time to run automatic at 60secs or manual at my discression.
RJ-
You are absolutely right, as long as the mis match is within that target zone the blending of hot/cold can be very pleasing to your ears. If spread becomes to far spread it's very noticable and rather unpleasant.. or just not right to the ear. Giving muddy lows or ice pick highs. Each amp has it's golden point of bias. some amps sound better right on the "it" spot others up or down. I personally try to keep matched tubes within 3% and if vintage big $$ NOS I'll use 5% if i have to. Anything over that is not good enough to go in my amps. Most of my amps are studio rentals so the tone matters... Which is why I purchased the Amplitrex.
