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6AQ5 tubes with adapter/converter to 6P1

 

Bronze Member
Username: Learners_permit

Post Number: 20
Registered: Jan-12
Hi

I have just received 12 x 6AQ5 tubes purchased from the USA and 12 x 6AQ5 to 6P1 tube adapter/converter from Hong Kong. Immediately I set it up but to my dismay there is no sound at all from my 6 speakers.
The 12 x 6AQ5 tubes inserted with the adapter are glowing which indicated that there is a connection.
The amplifier is a tube surround 5.1 channel which originally consists of 12 x 6P1 (Power tubes) and 6 x 6N2 (Voltage tubes). My only reason to upgrade those power tubes is to reduce if not remove the microphonics all together. I certainly not into what you expert out there call "tube rolling".
I did not upgrade the voltage tubes and could it be the main reason why it has no sound?
I have done some troubleshooting by replacing the original 2 x 6P1 tubes starting from the left (Centre speaker). There is sound dissipating from the Centre speaker. The amplifier is powered down and proceed with the same process replacing 2 more tubes with 6P1 this time from the right for Right Front speaker and there is sound.
Can anyone kindly advise what you think is wrong with the amplifier?
Or is it the tube or the adapter?
Any suggestion would be much appreciated.
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 17782
Registered: May-04
.

Let me get this straight; adapters = no sound, no adapters = sound?
 

Bronze Member
Username: Learners_permit

Post Number: 21
Registered: Jan-12
Hi Jan

I fixed the 6AQ5 tube with the adapter/converter to the amplifier which utilised 6P1 tube. The 6AQ5 is not a direct replacement for 6P1 and therefore I have to purchase the adapter/converter.
Yes after fixing the 12 x 6AQ5 tubes with 12 x Adapters/converters to the amplifier there is complete silence.
I then removed the 6AQ5 together with the adapter/converter one pair at a time with the original 6P1 tubes and there is sound coming from the Center according to the configurations. I powered down and repeat the whole process and all sounds are back to normal with 6P1 tubes.
I am not sure whether the adapter/converter is faulty or a design fault but how is it possible that all 12 adapters/converters not working at one time?
The 6AQ5 tubes is NOS and NIB. I can see the boxes are perfect sold by US seller on ebay: gtbs
I can't think of any other way to troubleshoot this problem.
 

Bronze Member
Username: Learners_permit

Post Number: 22
Registered: Jan-12
Sorry rephrase - "I then removed the 6AQ5 together with the adapter/converter one pair at a time and replaced with the original 6P1 tubes"
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 17784
Registered: May-04
.

There could be several problems, all of which obviously stem from a non-direct replacement tube being inserted into the circuit. If the replacement tubes show no signs of life, the best guess would be the two tube types do not share identical pin outs. If the tubes appear to be receiving some Voltage to the heater, the next most likely suspicion is insufficient Voltage/current to the tube.

I'm not familiar with the adapters you're using so I can't say whether your swap should be successful or whether the adapters might be faulty. It would be rather unlikely that all the adapters would be wired incorrectly or poorly. Therefore, I would have to assume this just isn't a swap meant to occur.

If the problem is microphonics, the better approach would be to tackle the issue at the source of the problem. What's causing the distortion? Can the system be set up for lower amounts of distortion?

Next, try isolating the amp with one of the many devices intended to float a component. Layers of MDF separated by layers of cork is a good start for a platform. A cheap but effective device for isolating tube amps is a racquetball. Two ways to use the ball, one is to buy a "bag of balls" - usually ten or twelve - snug up the bag to create an even layer of balls and toss it under your amp. The second way to use racquetballs is to cut them in half and place four or five under the amp. You can increase the effectiveness of this by heading to a hardware store's plumbing department. There are neoprene "Qwik-caps" which are used to cap an open pipe. They have a small depression in the center of the cap. Buy enough to match the raquetballs you are using and place the ball in the depression of the cap, then place the amp on top of the balls.





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Bronze Member
Username: Learners_permit

Post Number: 23
Registered: Jan-12
Thanks again for the reply.
The 6AQ5 has 7 pins and 6P1 9 pins which is the reason for purchasing the adapter/converter.

"If the tubes appear to be receiving some Voltage to the heater, the next most likely suspicion is insufficient Voltage/current to the tube."

Yes the tubes are glowing but not extremely bright due to the nature of the tube color which is black (6AQ5)Sylvania.

The Hong Kong seller has just replied that his engineer hand made 16 pieces of the adapter/converter of which 4 was sold to a French guy and he had no issues according to the seller.

I think you might be right that " the next most likely suspicion is insufficient Voltage/current to the tube."

Just wait and see or I might just ask for a full refund due to incompatibility.
 

Bronze Member
Username: Learners_permit

Post Number: 24
Registered: Jan-12
"f the problem is microphonics, the better approach would be to tackle the issue at the source of the problem. What's causing the distortion? Can the system be set up for lower amounts of distortion?

Next, try isolating the amp with one of the many devices intended to float a component. Layers of MDF separated by layers of cork is a good start for a platform. A cheap but effective device for isolating tube amps is a racquetball. Two ways to use the ball, one is to buy a "bag of balls" - usually ten or twelve - snug up the bag to create an even layer of balls and toss it under your amp. The second way to use racquetballs is to cut them in half and place four or five under the amp. You can increase the effectiveness of this by heading to a hardware store's plumbing department. There are neoprene "Qwik-caps" which are used to cap an open pipe. They have a small depression in the center of the cap. Buy enough to match the raquetballs you are using and place the ball in the depression of the cap, then place the amp on top of the balls."

Are you talking about vibration issues that could possibly caused the microphonics?
Do you think something like this link would do the trick?

http://www.decibelhifi.com.au/vibrapod-isolator/

or

http://www.decibelhifi.com.au/aamh-agora-acoustics-magichexa-each/
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 17786
Registered: May-04
.

It's pretty much a given that any vacuum tube will be microphonic to some extent. The advice given decades ago was to look for military tubes since they were generally designed and built for more rugged service. That's true - in some cases. The problem with military tubes is you can never tell what the tube was actually designed to do. If it was designed to deal with microphonics, it might have been encased in a piece of electronics which sat in a ton of cement five miles inside a mountain. Or it might have been designed for field use in communication services and sound quality was secondary to reliability. So unless you can narrow down more information on the tube you might as well just assume any tube you buy will suffer from some amount of microphonics.

You should determine which tubes are the most sensitive and possibly, if they are small signal tubes, you can add a tube damper. You can go to any shop that sells gaskets or most automotive shops sell high temperature rated Neoprene gaskets which will do everything a fancy tube damper will do for about 1/5 the price. Don't use any dampers on larger output tubes however. The temps are just too high.

But addressing the issue at the source is really your best bet. The problem is there is no single right answer to how to manage microphonics. Since each system set up will have different parameters, what works in one system might not in another. I've used the VibraPods and find them better suited to solid state gear such as CD players or pre amps. The other device you listed looks like a variation on placing bubble wrap under a platform you rest the amp on.

I would say the best route is to be creative. Think of ways to minimize transfer of vibration/resonance. Layers of several different materials - cork, foam board, MDF together for instance - make for a decent base for your amp. Each material is capable of resonating at a specific frequency which is not common to the other two materials. That makes it difficult for vibration to move between layers. Do a double layer of such materials and then place your amp on top of the base with some halved racquetballs under the amp and I would think you'll go a long way toward solving your microphonics issue at a bargain basement price. Of course, repositioning the amp will also make for less vibration entering the gear if you think this through.

Open cabinets are often not a good idea for tube amps because of the internal resonance they create. Lightweight trumps heavy since resonances pass quickly through light weight, rigid structures. Closed cabinets are worse since they simply represent resonating chambers very much like a musical instrument.

There are several threads in the archives of the forum which deal with isolating equipment. Check them out in the phono and amps section.




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