[HeyOK1000]

I'm using the Doge 6210 amp in the mindset of a trial period and most likely possible return. As I'm NON-techie I do not and cannot understand inconsistent sound volume changes related to EL84 tube rolling.

In using the power tubes that came with the amp, sound volume quantity is "appropriate" and even loud (with my AKG K701) at 9 o'clock. Even the volume varies with the 3 ohm selector. But quality rather harsh, as stated by other posters regarding this amp.

At first I tuberolled various vintage 12ax7s, finally settling on RCA Command 5751s to downgrade the harshness - all this using the supplied EL84s.

As recommended in this forum, for improved quality, I tube rolled the EL84s, using Amperex 1950s D getters, RCA blackplates and General Electric 60's ones. Yes, the sound got smoother but then came radical sound drops!

The Amperex got up to "near decent" volume - and not even that much at 2 o'clock - the bass starts to distort and in general, higher passages or crescendos distort as if the amp is being pushed too hard. The three ohm settings made little difference as all 3 sounded alike (different from the supplied tubes where it obviously varied). Even more startling, was that the big stage sound of the supplied tubes (with nice bass) recessed into the distance with the Amperex even though the "picture" was clearer. Singing voice was nice but and if the volume could have matched the supplied tubes everything would have been paradise!

There was a little more volume with the RCA and GEs - about 12 to 1 o'clock but still the same problem when cranking for more.

I switched back to the supplied tubes and the massive volume was back to "normal." When I tuberolled EL84s on other amps there was no volume discrepancy but definite improvement of vintage over current tubes. This is the first time I've ever had this situation.

Can anybody out there explain this? It is as if the supplied tubes were (to use an analogy) old highly efficient speakers used for flea powered tube amps and my vintage tube stock equaling 1970s speakers used with solid state amps.

I do want to say that I love this amp having absolutely NO HUM as opposed to the reconditioned single ended 6BQ5 amps I've experienced.

Thank you for your time and any and all replies.

 

[johna]

When tuberolling with Golden Dragon EL84 I`ve got the same problems.

A phonecall to Mr.Kvanild here i Norway, explained a lot of that to me.

The stock chineese EL84 tubes have a non functional 1. pin.
The 1. pin is the one to the 1. left of the opening between the nine pins.

The Golden Dragon EL84 have a functional 1. pin.

He told me that often the 1.pin is not functional on some russian and chineese tubes.

If you look with good light into the tube, you would clearly see if the 1.pin is connected or not.

So how is the tubesockets connected inside the the Doge?
Maybee the sockets have no connection to the 1. pin...?


This could possibly be an explanation on this problem we have?
Could this also be the solution in the big Doge thread?

PS:
I LOVE my Doge amp!!!
It`s so quiet and drives my AKG701 with bravura.

 

[HeyOK1000]

please excuse me, as I am not a techie I do not understand the tubes' pins stuff. As you've suggested I checked closely the innards of the pin's wires (1. pin and the rest) and cannot discern any obvious disconnection's. Mostly, (to my eyes) I cannot comprehend it.

Quote:

So how is the tubesockets connected inside the the Doge? Maybee the sockets have no connection to the 1. pin...?

Because of my ignorance, I did not even bother to look under/inside the chassis, as in all honesty I've would not understood.

However, I did set aside the stock tubes, inserted Sovteks (Russian?) and got that identical massive (volume) but forward sound. So you're right about the Russian and Chinese tubes having that similar pin relationship = synergy with Doge 6210. I wonder if the creation and manufacturing of the Doge was planned for these specific tubes in mind. But my problem remains as Russian/Chinese still has energetic but aggressive sound. The tubes would be perfect if it had that Amperex D getter natural sound.

Quote:

This could possibly be an explanation on this problem we have? Could this also be the solution in the big Doge thread?

If your explanation is correct, I do not understand the big Doge thread that influenced me to try this amp. That thread as I've reread did not state or address our problem. There was a poster who tuberolled the EL84s (with Amperex and others) and made no mention regarding volume inconsistencies. I am assuming that no other Doge owners have posted similar problems and replied to this thread because they've no old 50s/60s European and USA EL84s to tuberoll.

Quote:

I LOVE my Doge amp!!! It`s so quiet and drives my AKG701 with bravura.

I agree, the Doge is silent with no hum and it does drive my AKG K701 well (with just the stock/Sovtek tubes) but johna, what EL84 tubes are you using now?

Presently, I am waiting for a response from Pacific Valve regarding this situation. Again, any and all replies are welcomed and appreciated. Thank you.

 

[johna]

News about the EL84`s and Doge 6210

As written earlier, I have had many telephones and mails with Mr. Kvanild about this issue.
And this came to me today:
(With his permission)


DOGE 6210 STEREO HEADPHONE AMPLIFIER

To whom it may concern

Motron was asked by one of its customers to investigate why EL84 Golden Dragon performed very poorly in Doge 6210 Headphone amplifier. Normally Golden Dragon produces much better sonic quality than standard Chinese and Russian produced valves.(eg Sino, Sovtek and Elektro Harmonix).
The customer very kindly sent the amplifier to us and it was promptly put on the test bench.. Upon removing the bottom cover and taking a quick look at the EL84 socket the problem was solved.

SOLUTION:

The factory has used pin 1 on the EL84 socket as an anchoring point for other components. It is apparently not well known, but West European and USA produced EL84 valves have an internal connection between pin 1 and pin 2. This corresponds to the control grid.

Chinese and Russian production do not have this connection.

This means that as long as Chinese and Russian valves are used, the amplifier function perfectly, but if an W.European or USA NOS valve is mounted, the bias is drastically changed and performance becomes abysmal.
Golden Dragon also has this internal connection to pin 1, and I’m led to believe that although the valve is produced in China, it is produced to British specifications, and hence the same physical build up as the old Mullard valves.

MODIFICATION:

Simply remove the 3 resistors from the cathode complex of ECC83 triode 1. (3k; 68k and 100k) from pin 1 EL84 socket and resolder to a ceramic standoff glued to the chassis. This leaves pin 1 EL84 socket free, and we’re back in business

MEASUREMENTS:

Original configuration
Bias voltage (controlgrid – cathode) -6.2 V Chinese/Russian valves
-0.3 V Golden Dragon and NOS

Voltage across 200ohm cathode resistor EL84 6.5V Chinese/Russian valves
15 V Golden Dragon and NOS
After modification

Only normal variance between different valves was observed.

Voltages are of course approximate. Measured at 228V mains voltage

CONCLUTION

After completing the modification, the DOGE 6210 performs extremely well with NOS W.European and USA, Golden Dragon andChinese and Russian produced valves
We have so far tested Mullard, PhilipsHolland, Siemens, Telefunken, Ei, Tronix, Brimar, GE, RCA, Sylvania,NOS and Golden Dragon, Sino, Sovtek, Elektro Harmonix and Reflector 6P14P new production. Also several 7189 types.

The Norwegian distributor has been notified and he will relay this information to the factory.

Regards
Bryn
bryn@motron.no



So now I`m waiting for my 6210 to come back to me, with GD EL84 and the possibility to use all the valves that I want to try

Mr. Kvanild told me that he really like the sound of the Doge 6210.

I really hope this letter from Mr. Kvanild would explain the problems that some peoples have with this amp.

 

[sacd lover]

You could also just remove pin 1 .... which is much easier. Just make sure you have pin 1 before you snip the pin off.

 

[tbonner1]

Thanks for the update johna.

 

[johna]

Quote:

Originally Posted by sacd lover /img/forum/go_quote.gif You could also just remove pin 1 .... which is much easier. Just make sure you have pin 1 before you snip the pin off.

Easier, yes.
But the glass could easily break when cutting the pin, and beside, the valve would be useless in amps where the bias is connected to pin #1.
This connection is normal in many western amps.

As I wrote yesterday, now I can use all the EL84 valves out there

 

[drarthurwells]

deleted -duplicate post

 

[drarthurwells]

Take off the bottom plate of the Doge and turn upside down to look into the bottom, with the volume knob closest to you.

Look at the tube socket bottoms in the front of the amp - closest to you.

Note on the rear-right-sided pin with the gap to the left - with three resistors terminating and joined at that pin - that is pin number one and those are the three resistors referred to.

I don't understand this:

MODIFICATION:

Simply remove the 3 resistors from the cathode complex of ECC83 triode 1. (3k; 68k and 100k) from pin 1 EL84 socket and resolder to a ceramic standoff glued to the chassis. This leaves pin 1 EL84 socket free, and we’re back in business


Does this mean the connection to pin 1 can be cut, leaving the three resistors terminated together but disconnected from pin one of the two output tubes in front of the amp? Why then can't these three resistors with ends terminated together, just have these ends in free space (insulated with tape)? Why have them resoldered to a ceramic standoff (which I assume is not to ground the resistors)?

Also, will these voltage changes below cause problems?

MEASUREMENTS:

Original configuration
Bias voltage (controlgrid – cathode) -6.2 V Chinese/Russian valves
-0.3 V Golden Dragon and NOS

Voltage across 200ohm cathode resistor EL84 6.5V Chinese/Russian valves
15 V Golden Dragon and NOS
After modification

BTW a new Doge 6210 is coming out which will use a circuit board instead of point to point wiring. It will be interesting to see how it is wired to pin 1 of the output tubes.

I made numerous references in the Doge 6210 thread (link in my signature) to volume changes in the Doge that were tube dependent. I also pointed out that it was the combination of tubes that was important - I got great sound out of old American, Japanese, and European output tubes, as long as I matched them to the right 12AX7 input tubes.

My favorite combos now are two Russian 6P14P EB with two 12AX7 Groove Tubes or two Chinese 6P14 with two GE 5751. Neither of these combos would improve with the modifications of pin 1. I am worried the reverse could occur.

 

[sacd lover]

Quote:

Originally Posted by johna /img/forum/go_quote.gif Easier, yes. But the glass could easily break when cutting the pin, and beside, the valve would be useless in amps where the bias is connected to pin #1. This connection is normal in many western amps. As I wrote yesterday, now I can use all the EL84 valves out there

If you snip the pin you wont break the glass. The pin just has to be shortened enough so there is no contact with the tube socket. Secondly, unless you are going to use the tube in something besides the 6210 what difference does removing pin 1 make?

The circuit mod this amp needs is to rebuild the input circuit. I had my 6210 rebuilt with the best parts available. New signal caps, power caps, resistors, DH Labs wire, teflon tube sockets and so on. The sound was still decidely mediocre compared with my other transformer coupled tube amps, even with the superior parts and a signifigantly improved build quality. However, the 6210 with a completely revised/ rebuilt SRPP input stage .... is now excellent. The input circuit is what is limiting the 6210's performance.

 

[drarthurwells]

Quote:

Originally Posted by sacd lover /img/forum/go_quote.gif The circuit mod this amp needs is to rebuild the input circuit......... the 6210 with a completely revised/ rebuilt SRPP input stage .... is now excellent. The input circuit is what is limiting the 6210's performance.

Exactly what was modded in the input stage circuit to improve the sound so much?

Many would be interested, I am sure.

Also clipping the single connection of the three bridged resistor ends to pin 1 of the output (front) tubes, leaving the ends of the three resistors connected together (but wrapped with insulation tape) would seem to be the easiest solution (one wire cut on two tubes instead of many on many tubes) and would also would allow you to use your unmodded 6BQ5 or EL84 tubes in other applications.

 

[johna]

Hallo Doge owners and others.

Got a new mail from Mr. Kvanild:





DOGE 6210 A SEQUEL



I’m disappointed. When I wrote my first note on the DOGE 6210, I did so under the impression that people with at least a rudimentary knowledge of the operation of an electronic valve would understand the problem, and included measurements of operating voltages for the two scenarios to prove the point I was trying to make, namely that the 6210 is suffering from a design fault. Instead I find that some people are trying to treat the symptom rather than the cause.

Therefore I’m going to spell out in more simpler terms the PROBLEM, the CAUSE and one of many possible ways of CURING the problem



1: THE PROBLEM.



The 6210 performs very satisfactory with EL84 valves produced in China and Russia ( and it may well be that valves produced other places also will function OK as long as pin#1 is inactive)



The 6210 performs poorly with NOS valves of western European and USA production. Also with the new production by Golden Dragon.(which indeed sparked off this investigation.)



2: THE CAUSE



The factory has used pin#1 of the EL84 socket as an anchoring point for three resistors which in reality have nothing to do with the EL84 at all, but are part of the cathode complex of the input triode half of the 12AX7/ECC83 valve.

As long as the afore mentioned Chinese and Russian valves are used, this works fine because on these valves pin #1 is totally inactive (not connected to anything at all)



The operating condition of the EL84 will remain as the designer intended.



In the amplifier I investigated, using chinese and russian valves, the control grid – cathode voltage was measured to - 6,2 Volts and the voltage across the EL84 200ohm cathode resistor was measured to 6.5 Volts. This gives an operating current of approx. 32mA (this is the combined anode and screen grid currents) Consulting the data sheets of the EL84 this seems to be a fair choice for the operating point.



If however a NOS western European or USA produced EL84 is used, the situation changes dramatically. This because these valves have an internal connection to the control grid from pin#1. The measurements for this scenario shows a bias voltage of – 0.3 volts. And the voltage across the EL84 cathode resistor measures 15 volts giving a total EL84 operating point current of approx. 75 mA. !!!!



This is definitively NOT what the designer intended.



Therefore I'm surprised at the reports of alleged fair sound quality with Mullard, GE and such NOS valves in an unmodified amplifier.



3: THE CURE



If you are satisfied with the sound quality using EL84’s of Chinese and Russian production: DO NOTHING!



If you would like to “tube roll” with all available valves from the EL84 family, read on!!



Remove from pin#1 EL84 socket the three resistors connected there. ( they must remain coupled to each other). In fact since there is only one wire from the resistors connected to the socket pin, you can just snip off this wire.. No soldering required. Make sure that the end of the three resistors which are still connected together and sporting an approx. 10mm long wire stump cannot short circuit to the chassis or any voltage carrying wires or connections.



This you can do in any way you like.



I chose to connect the single wire from the three resistors to an insulated standoff fastened to the chassis instead of leaving them waving in the air.



Basically the whole modification is in fact snipping off the wire to pin #1 of the two EL84 sockets



You can also , as was suggested, snip off pin# 1 on the EL84( and ruin a perfectly fine and expensive NOS valve) If you do that, you can leave the three resistors be.



The modification will of course not influence in any way the operation of chinese and russian valves.



If you do the modification, try Mullard old logo EL84 together with Mullard M8137(box anode, long life, extremely low inherent noise) Exquisite !!!!



regards


Bryn.





Mr. Kvanild and I don`t want to make a “war” here.

He just wants to explain us what he see in this amp.

 

[drarthurwells]

Yes, pin 1 of the EL84 or 6BQ5 tubes is dead - inactive - not functional.
However, internally it is connected to pin 2 which is very active. This is not the case with Russian or Chinese tubes (except the Golden Dragon) where pin 1 is not wired to pin 2 inside the tube in manaufacture.

The reason to wire pin 1 to pin 2 inside the tube is to allow for more external parts (resistors, caps) to be soldered to pin 2 simply by soldering them to pin 1 instead of 2. Some designs make use of this and solder to pin 1 as equal to a pin 2 connection.

Just cut off the wire to the front tubes of the Doge, where three resistors terminate to a pin, and leave the three resistors connected together, then tape to insulate these three. This will leave the pin bare. I will be glad to do this for free if anyone wants to pay shipping both ways - takes a few minutes.

Then front output tubes that have an internal connection between their pins 1 and 2 will perform better.

I have got good performance, with volume decreases, with old American and European tubes, with my Doge before cutting pin 1 connections. The reason is matching them with the right 12AX7 tubes. Now in cuting the three resistors away from connecting to pin 1 it will be much easier to match with more 12AX7s and get good sound with more volume.

I have repeatedly advised that the tube match, between input and output tube types, is the thing. This is as important as any mod you can make in getting good sound.

 

[drarthurwells]

Quote:

Originally Posted by sacd lover /img/forum/go_quote.gif The circuit mod this amp needs is to rebuild the input circuit. I had my 6210 rebuilt with the best parts available. New signal caps, power caps, resistors, DH Labs wire, teflon tube sockets and so on. The sound was still decidely mediocre compared with my other transformer coupled tube amps, even with the superior parts and a signifigantly improved build quality. However, the 6210 with a completely revised/ rebuilt SRPP input stage .... is now excellent. The input circuit is what is limiting the 6210's performance.

Could you please describe the design mods you had done to rebuild the input stage of the Doge 6210?

This sounds exciting.

 

[teros1]

Mr. Kvanild, you have the sincere thanks of myself, and I'm sure many 6210 owners worldwide. This is very valuable knowledge.

(Thanks also to cotdt, johna, sacd, et al as well.)

Conspiracy theory: Maybe the Chinese government mandated the design, to help spur consumption of Chinese tubes....

Bob