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Tube Matching

T

Tonedeaf

Active Member
It has come time to replace/roll the tubes in my Dared VP16 integrated amp. I am using four generic chinese 6V6 output tubes and two 6SL7 tubes in the preamp now.
I have read about the benefits of matching the 6V6 power tubes, but is there any benefit to matching the 6SL7 preamp tubes?
 
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Thanks for the reply.
I have been getting a nasty hum lately and thought it would be a good time to upgrade the tubes. I have a matched quad of Phillips JAN 6V6GT's coming and need to order the input tubes but was not sure about matching these too. Thanks again! :thmbsp:
 
Front end tubes are almost never run to there limit in a amplifier or a preamp so there is very little benefit to matched tubes. However in a push pull amplifier with say a longtailed pair phase splitter setup that uses both halves of a dual triode a matching set of tube is advisable. Especially if there is no provisions for AC balance. Much of the distortion that you hear SET fans complain about in Push pull amps are from designs that do not carefully implement the phase splitter and have output tube setups that don't afford absolute balance to the output stage. I personally always prefer matched tubes for output and matched section on dual triode used for phase splitters. So the answer to your question is it really depends on the topology of the amp in question.
 
NOSValves- You pretty much lost me after... "Front end tubes are almost never run to there limit in a amplifier or a preamp so there is very little benefit to matched tubes." LOL
I don't know anything about the make up of this little amplifier other than it it makes some pretty nice music! Or it used to.
I appreciate your reply and I am learning as I go. Thanks for bearing with me!
 
Ryan C. Inman said:
If I'm not mistaken, these new Dared models use a simple Cathodyne type splitter, with one triode section and equal plate/cathode resistors.

This type of circuit has no gain at all, it is unity gain. This would also mean tube matching for this type of circuit is worthless.

-Ryan
Click to expand...


If that is the case then your absolutely right. But are we sure?
 
Actually a good number of amps coming out a China are Longtailed pair phase splitters. Even the Chinese have realized it the best overall phase splitter if balanced properly. Cathodyne is just cheaper and easier to implement. But as far as Dared I'm not sure what they used.

Craig
 
I believe the dared stuff is all circuit board so its pretty hard to tell what it is form a picture but if you post it I'm sure we all will look it over :)

Craig
 
Here's a pic anyway. For all intents and purposes, matching the pre tubes wouldn't hurt, just might be unneccesary depending on how the amp is wired. Correct?
 
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I'd get matched if I was you. Although this amp having only one input tube per channel has the be a cathodyne phase splitter or similar. Having the two tubes 4 triode section fairly closely matched will insure balance between channels. Matching can never hurt (in some cases is required) no matter what the circuit consists of electrically.

Another thing I notice is there seems to be bias controls under the chassis. Does your manual give you any instructions on biasing the output tubes. It would be benisicial to have the outputs perfectly balance even if you buy a matched quad. In reality there is no such thing as a perfectly matched quad by the way. I bet those 4 white cement type power resistors at the edge of the PC board are cathode sensing resistors for measuring biasing. This is a very good thing!!


Craig
 
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Well, if it won't hurt anything, I'll pay the extra couple bucks and get a matched pair for the input as well.
There are no instructions on setting the bias in the manual. In fact it states that there is no need to set the bias when replacing tubes. I am not a tech, but I kinda thought that's what those POTs would be used for as they appear to be attached to the ring of solder joints for the tube sockets. Time to search AK for biasing an amp! Thanks again for all the info and insight. Very helpful.
 
Write Dared and ask them what the bias should be set at ! Audcom and Cayin did the same thing but the bias was adjustable and you will benefit from lower distortion and extended tube life with the outputs perfectly balance. The quirk on this is if it really have cathode sensing resistors. If it doesn't there is no method to accurately test the bias for each tube anyway. Heck see if they will send you a schematic !! Send it my way and I will figure it out for you and walk you through setting it.

Craig
 
well, that e-mail went straight to China! No US contacts. Hopefully they can set me up with specs and a schematic.
 
If worse comes to worse tell them the amp broke down on you and a local tech offered to fix it for free but he needs a schematic amd wants this information before he will work on it.

Craig
 
As far as 6SL7s go I have found the best for my amp to be RCA VT-229s followed by Syllvania VT-229 and the short brown based Syls. The lshort Syl brown based might be the best buy, the VT-229s are gettinh hard to find.

Guitar players like the old RCA graphite sided 6V6s but I never have had a 6V6 amp to roll any in. I have lots of pulls though that I have kept as they are supposed to be great sounding tubes.
 
Still waiting for a reply to my e-mail to Dared, China but I couldn't wait.
I installed a matched quad of Phillips JAN6V6GT and a matched pair of Phillips JAN6SL7s. One of the output tubes glows slightly stronger than the other 3. I don't know how the old tubes looked because they were black glass. I am not sure if I should be concerned or not. It sounds better, ie... the hum and crackle is gone anyway.
 
The part that glows in the tube is the heaters and if the elements on one tube are exposed further then the rest you may see more glow. I wouldn't worry about it unless what is glowing is the actual biggest grey structure inside the tube. This is what is called the plates and should not glow at all.

Craig
 
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