6P14/EL84 amplifier kit building questions - before I build - maybe during if I do

[Never Get Old]

Some, mostly eBay sellers, would have you believe that the Russian 6N1P is similar to and a drop-in replacement for the 6DJ8 family of tubes. IT IS NOT!

Yes, I found that out with some research. 6DJ8 may or may not work in some applications, but it is not a good idea unless specifically recommended by a manufacturer.

Research on the Chinese 6N1:

1. Supposedly 6N1 (China) = ECC85 = 6AQ8 (NOT 6DJ8). The amplifier schematic and circuit board both say ECC85 on them. The kit comes with 6N1, which I suspect is being used as a cheaper substitute for the ECC85 and may not be an exact equivalent. The manufacturer of the amplifier kit recommends changing them to ECC85 for "better sound."
2. Supposedly 6N1P (Russia) is not an exact replacement for 6N1. I don't know why.
3. I found the actual data sheet for the 6N1 (China), but it's in Chinese. Can anyone here translate Chinese to English? I am asking a Chinese manufacturer if they can provide it in English.

Note: I thought I would feel awfully silly if I don't actually build this little amplifer but put in all this work. Then I remembered that it's a valuable learning experience to do this research and discussion, plus a public service if it helps anyone in the future.

Someone please see if you can perfect the attached Word document for the Chinese translated 6N1 specs. It is the best translation I can do for the actual 6N1 (China) - line by line with Google translate. Perhaps someone with knowledge of standard tube specs can help me finish the translation to English? Some values should be obvious to those with experience. The spec charts are in it along with numerical values. Also in the document are the Philips (1969) ECC85 and Russian 6N1P specs.

Thanks!

 

[Never Get Old]

You won't get an accurate read on filament voltage until all tubes are in and B+ is applied (the PT is loaded down).

Yes, xraytonyb confused me on that a number of times.

The Russian 6N1P is, from all reports, nothing like Chinese 6N1.

I can't confirm those reports. I downloaded and partially translated the spec sheet for the Chinese 6N1 and am asking for help finishing the translation. The Word doc I posted earlier contains the actual specs for the 6N1, 6N1P, and ECC85 if someone can help perfect that document for everyone to use as reference/proof.

Referring to this earlier post, that looked like quite a neat drawing tool for doing the layouts - which one is it?

I did that in my old version of CorelDRAW. I do a lot of graphics for model trains, and I have been using CorerlDRAW for about 25 years now.

 

[Never Get Old]

Since the tube amp needs a load on its output transformer you would also have to have a dummy load that is switched out when the speakers are connected. If you are thinking that part is only applicable if the tube amp is on, then it is quite likely you might switch it on with the switch in the wrong position, so it is shrewd to consider the potential pitfalls.

Oh, I had not thought about that problem. If I turn on the tube amplifier and the amplifier selector switch is in the wrong position (it set to the transistor amplifier) then the tube amplifier would have no load. That could be a problem. However, I am quite sure that I have turned on my Dynaco ST-70 series II many times over the decades with no load attached when testing it. If this is so bad, why has nothing ever gone wrong with it? Why must there be a load, and what happens if there is not?

 

[Kay Pirinha]

If you don't want to use the kit's gain/phase splitter tubes but don't want to spring for ECC85s, 12AT7s are kinda, sorta a 12 volt equivalent. You'd have to rewire the filaments though.

12DT8 is an even closer 12AT7 equivalent. It just leaves the heater middle unconnected. Quasi an 12.6 V ECC85 without shield.

However, I am quite sure that I have turned on my Dynaco ST-70 series II many times over the decades with no load attached when testing it. If this is so bad, why has nothing ever gone wrong with it? Why must there be a load, and what happens if there is not?

You just had luck, as you supposedly didn't drive this amplifier. A quiet, stable amplifier is not that prone to get impacted by an open load condition. But if you drive it, the OT's primary inductance will produce undamped voltage surges that may destroy the tubes, the holders, or in worst case even the OT.

Best regards!

 

[Never Get Old]

You just had luck, as you supposedly didn't drive this amplifier.

Correct. I have never operated the amplifier with music input and no load. Thank you for the word of caution about having an amplifier switch set to the wrong position. I never would have thought of that. I would have to be careful. No way to avoid it except to be careful I guess, even if I manually switch the wires at the speaker terminals to switch amplifiers, I could still accidentally not have the proper amplfier connected.

I am still waiting for various info from Chinese sellers about this amplifier and the tubes. I found and translated a "new product announcement" for the Chinese 6P14:

6П14П (6P14P) output pentode changed to a new model 6P14 after 64 years.
The 6P14 tube is a side-heat pentode tube.

The new domestically produced 6P14 is an optimal tube with international advanced level. Its birth marks the rapid development of electric vacuum technology in my country (China) and creates favorable conditions for the future production of high-quality loudspeaker equipment and recording equipment.

It then goes on to state exactly the same specifications as the 6P14P. Hmmmm ... maybe he just did a copy and paste?

Comments on the announcement:

6P14 is designed for high-quality power amplifiers. Its advantages go without saying. The sound of domestic tubes is actually good. The disadvantage is that the parameter variance is relatively large. The workmanship of the Shanghai tube is poor.

The Telefunken EL84 is far more beautiful than the 6P14 in the mid-frequency and high-frequency, and the high-frequency is gorgeous and particularly noble.

The sound quality of Beijing brand 6P14 is much better than other brands, even slightly better than imported original EL 84, 6BQ5, 61411, no wonder many audiophiles flock to it.

 

[Kay Pirinha]

...whatever side-heat pentode means ...

Best regards!

 

[Never Get Old]

...whatever side-heat pentode means

The Russian translation for the same thing is, "Cathode: indirectly heated, oxide-coated" plus the Chinese and Russian translation "output pentode"

I run into minor problems like these when translating recipes from Chinese websites.

 

[Chris Hornbeck]

The danger issue of any vacuum valve amplifier with an output transformer WRT loading is one of over-voltage damage to insulation within the transformer, or if really terrible, within the valve itself. What could cause such a high voltage? Fundamentally, a large di/dt across the output transformer (OPT)'s primary windings, or said another way, a large voltage spike across the winding(s) as a significantly large current collapses significantly rapidly.

An amplifier operating well within its design limits, hi-fi mode, comfortably below clipping, will never see these conditions. But a heavily overdriven (guitar amp style) amplifier, or an oscillating amplifier (and many normally well behaved amplifiers behave poorly or unstablely in overload), or a perfectly good amplifier in heavy overload party night style, might. The single thing within the designer's control is stability with varying loads and varying signal levels. Zobels = snubbers = damping.

Rock and Roll,
Chris

 

[wg_ski]

Don’t use your good hi-fi amplifier for “party night” unless it was designed with overvoltage protections in mind. Yes, any of the standard treatments can have an influence on the sound (usually not for the better - just like adding SOA protection to your sand amp can have a negative influence so you are tempted to omit it). If anything else, it gives one a valid excuse to build more than one amplifier.

 

[Never Get Old]

If anyone wants the building instructions, download them now while available:

https://drive.google.com/drive/fold...S?spm=a2g0s.imconversation.0.0.2acc3e5fdxykKS

It's the original manual used by xraytonyb in his three-part video build. Another seller has told me that the loudness circuit has since been removed from the later production of the kit. I can't confirm that unless I buy one and see what comes in the box, but one seller did tell me, "Dear friend, this function now stopped" when I asked about the loudness switch.

 

[Never Get Old]

Not that I have any intention of buying this version, but they now offer the same kit with a USB port and bluetooth. I think it also has an FM tuner. I guess it would be convenient for someone who wants a tiny, tiny system, which I do, but not with bluetooth and USB inside my amplifier! That should be a separate box IMHO.

Any suggestions for a cheap and small tube DAC kit that I can use as a preamp, or just a small tube preamp, for use with my Dynaco ST-70 series II while I wait to see if I am going to build this kit? Must have volume control because the Dynaco does not. I figure a tube DAC with volume control kills two birds with one stone.

 

[OldHector]

The USB and Bluetooth is just a tiny PCB. I don't see why it is an issue having it inside the same box?

Perhaps you should start an alternate thread looking for a tube DAC now that you have changed tack in your thinking?

 

[Never Get Old]

Perhaps you should start an alternate thread looking for a tube DAC now that you have changed tack in your thinking?

I haven't changed tack, and I may start a new thread on the DAC topic.

• I'm waiting for more information about the little integrated amp from China and figuring out what to do as a temporary solution.
• I just got the directions for the integrated amp kit from China today (see earlier link).
• I'm still asking the folks in China which versions still have the loudness control. One seller says theirs does not.
• I made an offer on one earlier today.
• I have done a lot of research on the tubes involved (see earlier post) and would like some help filling out the incomplete info on the spec sheets that I translated (partially) from Chinese.
• So, I haven't changed tack, and I will be presenting more information and questions.

 

[OldHector]

Just saw your updated reply, so my question is moot. I do not see where a tube DAC fits into this thread, however.

 

[Never Get Old]

1. Enormous variation in price, including one seller who just doubled the price. I put an offer on one today. Awaiting response.
2. Confirmation on the loudness control issue. If there is a version without it, I want that version.
3. I just got the directions a few hours ago. I wanted to see if they were updated. They are not.
4. I have been very busy. Life.
5. I am now pulling out of the cabinet my Emotiva processor and Outlaw Audio amp in preparation for selling them, and rewiring everything with a used Denon receiver temporarily. It's a huge job to pull out the entire system and rewire everything as I prepare to downsize. I retreived the shipping boxes for the Emotiva and Outlaw yesterday so I can now sell them to finance the project.
6. Figuring out the feasibility of having both a surround receiver and the 2-channel tube amp at the same time. Thank heaven someone warned me about the risk of a no-load accident. I am looking at switches where I could wire in an 8-ohm load inside to protect against that to see if that's possible.

 

[OldHector]

The loudness switch is likely just a switch that adds or removes a passive band pass filter. The switch might be useful for other purposes if you don't like the loudness circuitry, for instance use it for mute or disabling the magic eyes. What is your concern about it?

If you build the kit as it is (with PCB) then you quickly get the amp you want, and then you can revisit it and wire P to P later, if that takes your fancy. For the money you get mostly the same hardware for any variant, and having the case ready to go is a great asset.

So then it just boils down tot he cheapest supplier who can deliver in less than 90 days, if this is Chinese post.

 

[Never Get Old]

The loudness switch is likely just a switch that adds or removes a passive band pass filter. The switch might be useful for other purposes if you don't like the loudness circuitry

If you watch xraytonyb's video series on the amp, the loudness is a horrible and complicated design, revolving around a really bad potentiometer that cannot be left in the circuit. He immediately removed it. At the same time he put in an Alps pot and added 2 resistors to keep the inputs from going to ground when the pot is at zero.

So, here I sit with a pending offer that I have to wait to expire before I can make an offer to another seller.

Add to my prior list of delays:

1. Spending days re-learning what I have forgotten about amps and tubes and asking questions here - to ensure that I can be successful in this project.
2. Chinese New Year meant that I could not get any answers at all out of China until they returned to work Tuesday of this week.
3. Temporarily wiring in my Dynaco ST-70 series II so I could determine if the return to tubes after 10 years of solid state is really something that I want to do.
4. Figuring out temporary solutions because it will take at least 2 weeks to get the kit and then several more weeks to build it, plus any upgrades that need to be done so I have to order parts. I'll be asking questions on that too. I won't know what's in the kit until it's in my hands as they change the parts frequently.

 

[Koonw]

I have edited 6N1 data.

 

[tbaashus]

I've built this amplifier. Actually I've built two. I sold the first one, but regretted it and built a new that I have now. It may be a cottage industry product, but the quality of the parts are quite good. I don't think there should be any problem with tube rolling unless the tub unless one is very brutal while changing tubes.

The building instructions are very good and detailed and easy to follow with help from Google translate. The amplifier doesn't come with a loudness circuit anymore. I can send the instruction to anyone interested. Just PM me.

And, the amplifier sounds very good, so well worth the effort.

 

[Never Get Old]

I can send the instruction to anyone interested. Just PM me.

If you have new instructions, please send as I only have the old ones with the loudness circuit. Thanks.