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Robin H
Reply with quote  #16 

Yes. I will.
I'm traveling and it will take a while to get the JJ tubes.

If you can't wait, I would suggest you just go with JJ.
Definitely no GL PX300b on Pinnacle- we learned it in a hard way...

Robin H
Reply with quote  #17 

A quick up date:

Got my JJ 300B installed last night.
4 tubes are all factory tested with the same value.
However, at first installation. Bias can't be zeroed. Output is -0.1V even when the pod is turned all the way clockwise and the amp blow fuses when driving hard.
After I swapped V4 and V6, bias can be set to around 0.03V and then it worked fine.

I had only 3 hours on it.
They sound very good right out of the box.
Did not do serious AB comparison as it might get better after broken in.
Basically, I'm pretty happy with it.
First impression: It is pretty balance from low to high. Very good detail.
GL PX300B (similar price) has a little more body in the mid range and less high extension.
PSVan (half the price) is brighter, less body in the mid.

I found the big transformer is significantly hotter than running with PSVan or PX300B tubes.
It is too hot to put my fingers on it for more than a second.
I have not yet measure the temperature or the current through the plate resisters.
I'm wondering if the JJ is running drawing more current at the same bias.

It would be greatly helpful for users, if someone can provide a procedure or instruction on
- How um-matched tubes affect the amp. How far we can go if not matched?
- How to swap tubes to balance out the un-matching.
- I guess V4, V5 shall be matched and V6, V7 shall be matched. Is it less problem if V4/V5 don't match with V6/V7?
- Swapping V4/V5 or swapping V6/V7 doesn't make a difference, correct?


Reply with quote  #18 

You should always buy tubes matched for current. But normally they are matched at a different voltage/bias than in  your actual amps and they will not 100% match in your amps. In most cases this shouldn’t become a problem as little fluctuations can be handled and are normal.

As I have already mentioned in an earlier email you need to swap tubes –one at a time - and adjust the DC offset every time and find out whether it gets lower and more stable. That's the only way to make them "share" current in between more equally if one or more tubes are stronger than others and simply conduct more than the rest. As you can only adjust bias for one power rail with the DC offset pot (the other bias is set) you need to swap tubes if adjusting offset doesn't give you good results. Some PP amps have pots for both power rails but even then it’s impossible to match the tubes 100%. You would need one bias pot for each tube which can be adjusted separately from the rest or autobias where some electronics do this job continuously.  The Tentlab autobias doesn’t work with TS products, just FYI, as it needs ground as reference and the TS output is floating. Tentlab is working on a new autobias but it will take them a while.

I would also measure if the bias voltages are ok. If your transformers for B+ are running too hot it means that there is too much current through one or more tubes (idle current too high, one stronger tube hogging too much current). In an extreme case one tube could be red plating (anode too hot) and fuse would blow.

Tubes of the pos  need to be matched as close as possible to neg side in a PP amp. But also the position of the tubes on one side can matter (between 4 and 5/6 and 7 in your example) in order to achieve this. The rest you can adjust with the DC offset pot. So simply start with 7 in position 5/5 in position 7. Then swap 5 with 4 and adjust offset again. If not good enough swap 6 with 7 (former 5) etc. Without tube tester this is the only way to solve this problem. If all this doesn’t help, the tubes are current matched,  and your bias voltage is ok there must be a different problem causing the overheating of the transformers.

Reply with quote  #19 
With the Pinnacle on my wish list this is what I found ... 500US$ approx

Part of the hold up on this entire review has been, well, just as i found a killer tube like the Valve Art, another tube would come along and blow all others away when used as a direct normally electrically run 300B. These new JJ Electronic 300B tubes made in the Slovak Republic have won my heart as the all out winner of this grouping in my systems to my ears.

Although a bit microphonic, it seems to have the best balance of smooth mids with upper and lower frequency extension in my beloved Wavelength Audio Cardinal amplifier.  If fact i love it so much it now pretty much permanently resides on it as part of my main reference system, only giving way to the WE300B when i desire a more, um, seductive sound.  Ambience and imaging are excellent as it inner resolution too!  This is the latest 300B to arrive here in my humble abode and also the best so far for direct replacement on a normally run 300B amplifier.   Some of you might worry about a bit of that blue glow on the top, but then again so did the WE300B have that at the beginning too.  i feel there is just too much emphasis on that top blue glow.  Yes, it does mean a few things, yet it's not necessarily gonna make your system sound like junk, burn down a small village, and release a nuclear warhead on your government.  Sheeesh, relax and enjoy the music!

The JJ Electronic 300B seems to have all the things i love about 300B tubes!  What more can i say then that?  May i humbly suggest you try the JJ Electronic 300B?   You too might find yourself in love while enjoying the music.

Reply with quote  #20 

Hi (Robin),

I did measurements for you with combinations of three companies:

300B KR
300B JJ

JJ's measurements with the speakers show the same thing.

Only two additions / questions:

1. Who built the amplifiers for you?

2. Recommend you, because you make frequent breaks between the uses of amplifiers:

Turn on:

Source, pre-amplifier, after 2 minutes the amplifiers.

Turn off:

Amplifiers, after 30 seconds Pre-amplifier, Source.


Good luck to everyone,



Attached Images
Click image for larger version - Name: 300B JJ.jpg, Views: 75, Size: 308.45 KB  Click image for larger version - Name: kr 300b + 300B JJ.jpg, Views: 76, Size: 170.81 KB  Click image for larger version - Name: PX300B + 300B JJ (2).jpg, Views: 77, Size: 173.84 KB  Click image for larger version - Name: PX300B + 300B JJ.jpg, Views: 70, Size: 260.63 KB  Click image for larger version - Name: PX300B + KR300B (2).jpg, Views: 72, Size: 185.13 KB  Click image for larger version - Name: PX300B + KR300B.jpg, Views: 65, Size: 147.74 KB 

Reply with quote  #21 
Hello dear all,
Can I conclude from all this, that building the Pinnacle is way too difficult and risky for someone with no knowledge of electronics?
Did any of you ask Bruce about this? To me,I may be very wrong,this sounds like a serious problem..

Thank you for your replies!

Reply with quote  #22 
Hello Gaston - what exactly do you mean?

Except for the necessity to avoid mesh plated tubes (which Bruce points out in the manual) and the recommendation to get matched quads, there is no special knowledge required to build the Pinnacles.

I have run mine with four matched pairs of Shuguang 98's without a problem. After about 2000 to 2500 hours I checked how the amps sound with fresh matched quads and found negligible difference. So even the 300Bs lifetime in the Pinnacles is quite extensive.
Kelvin Tyler
Reply with quote  #23 
My experience with the Pinnacle amp closely follows that described by Achim. I believe I was one of the first to build this amp over 18 months ago and it has not missed a beat over that time. In my case I used matched pairs of Electro-Harmonix 300B EH tubes with excellent results. As with Achim my Pinnacles still sound as good as when they were first run in. This is an amp that lives up to its name.
If you can solder, there are no special problems in the build. The instructions are clear; there is just quite a bit of it! Most of the previous comments relate to after build tube choice and set up.

Robin Ho
Reply with quote  #24 
Thank you all very much for the help.

I think I have identified the problem: It is the high capacitance speaker cables!  I'll explain it in detail later.

Ben, Gaston: I built the Amps myself.  With some DIY experience, the Pinnacle shall not be difficult to build. The step-by-step manual is clear, detailed with photos.
I've been a DIYer for 30+ years and have built a few amps from stretches.
However, it is the first OTL amp for me. Its circuit design is very different but is not very difficult to build.
During the process, I had a bad socket, burnt a driver tube (my own tube).  Bruce helped me out Via e-mails.
Also, I have traced every steps of the instruction and photos back to the schematic to double check and found some inconsistency which I clarified with Bruce Via e-mails.
However, Bruce has no idea of why it keep blowing fuses.

Here is the latest report:
The JJ 300Bs still not work at loud passage when driving my main 2-way speakers.  It still blow fuses but less often than the GL PX300Bs.

So, I left the main speakers along and use the Pinnacles to drive my full range speakers (8 Ohm 93db) in the past months.  It works well. No blowing fuses.  I'm using 5 meters long, DIY Cat-5 speakers cables (Designed by Chris VenHaus) which I used for all my speakers.

My main speakers are 2-way, MTM design with 2 x 5-1/4" mid woofers, passive crossover, 4 Ohm, around 88db.  Pared with active crossover woofers driven by 120W PP tube Amps.
I know 4 Ohm is not the ideal speakers for OTL tube Amp. But I have no other choice at the moment. So, I use ZERO-autoformers at 4X connections so the Amps would "see" the speakers as 16 Ohm.
The autoformers are close to the Amps and connect to the Amp directly.  The speaker cables are connected from the autoformer to the speakers.

Today, I had the time to re-visit the issue and re-read the Zero-autoformer manual. It says the autoformer shall be located close to the speakers as possible. Bingo!
The problem is the Cat-5 speakers cables. Those are high capacitance cables. When connected between the autoformer and speaker, it "reflects" the capacitance 4X times back to the amp!  I was using 5 meter long, bi-wiring cables which makes the capacitance even higher.
I just replaced those high capacitance Cat-5 cables with regular strained speaker cables and the problem almost gone. Only blow fuses once. After 3 hr. break-in, it gets more stable.
I'll give it some time to break in to see if I need to move the autoformer further closer to the speaker which will make bi-wiring impossible....


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