[jlafrenz]

I recently picked up a Decco 2 and decided to try a couple of different tubes in it to tailor it to my tastes. I see that 6N1P tube are in the same family of the 6DJ8 so I picked up a tube at a local shop to try out. As soon as I turned it on, there was lots of distortion and crackling so I shut it off to avoid any damage to the unit. The shop said they tested the tube, but I figured one may have slipped through. I have some other 6DJ8's laying around so I tried one of those and had the exact same issue. So now I am wondering if it is the tubes I am putting in it or the unit itself. What might be causing this or what am I overlooking?

[JakeJ]

Hi jlafrenz,

Welcome to AC and the Tube-O-Phile circle!

Does the tube(s) that came with it have this issue?  I know nothing about the Decco units, other than the aesthetic cool factor.  It does seem odd that it won't work with the tubes you mention but there are differences in the three types and it may be that only the 6922 will work.

Hopefully someone that has direct experience will chime in.

[jlafrenz]

The factory tube works just fine. It was my understanding that tubes in that family could be swapped for each other. I guess that may not actually be the case and is why I am seeking some advice from those more knowledgeable.

[bunnyma357]

I don't have the actual specs in front of me, but I know the 6N1P is "similar" but not always a suitable substitute for the 6DJ8 family - it depends on the circuit.

The Russian equivalent of the 6DJ8 is the 6N23P tube.


Jim C

[JakeJ]

It may be that the Decco 2 is designed for the 6922.  You could get a few to try, or at least one to confirm that that is the issue.

Roger Modjeski has stated in his Music Reference circle that he has just recently gotten a batch of the best 6922 he has ever seen.  Here is the thread and the exact post (last paragraph) http://www.audiocircle.com/index.php?topic=84189.msg841365#msg841365.  Might want to get one of those.

[Wayne1]

While the pins do the same thing for a 6922 and the 6N1P, the current required for the filament circuit of the 6N1P is twice that of the 6922. You should not use the 6N1P unless you know for certain the filament power supply is rated for such a load.

The 6922 has a filament draw of 0.3 amps. The 6DJ8 is 0.365. The 6N1P is 0.6

[jlafrenz]

While the pins do the same thing for a 6922 and the 6N1P, the current required for the filament circuit of the 6N1P is twice that of the 6922. You should not use the 6N1P unless you know for certain the filament power supply is rated for such a load.

The 6922 has a filament draw of 0.3 amps. The 6DJ8 is 0.365. The 6N1P is 0.6

Thank you for the insight on my tube situation. The stock tube is the 6N1P so I am good to go with that tube. I just wanted to try out some others to smooth out the sound a bit more. Looks like I will have to start some research on 6N1P's.

[bunnyma357]

My Yaqin MC-10L integrated uses 6N1P tubes and I swapped out the stock Chinese tubes with NOS Military Grade Russian Voskhod (Rocket Label) 6N1P-EV tubes and have been very happy with the results.

The Voskhod tubes can be found from US distributors, or you can buy them on eBay from Soviet countries, which is what I did.

http://www.cryoset.com/catalog/product_info.php?products_id=251

eBay Seller (No expperience with - just an example):
http://cgi.ebay.com/6N1P-EV-ECC88-6DJ8-MATCHED-PAIR-tubes-VOSKHOD-NOS-1989-/130443921119?pt=Vintage_Electronics_R2&hash=item1e5f1046df#ht_974wt_859


Jim C

[Mike Nomad]

Not much by way of direct experience... this thread caught my attention because I just replaced the tube in my Nova.

I find it interesting the specs for the Decco 2 call for a 6N1P, while the Nova has a 6922. My original, stock tube went bad, and I replaced it with a vintage 6DJ8. Major sonic improvement.

[JakeJ]

Looks like I was wrong because the website I looked at said the 6922 is the stock tube, not the 6N1P.  My apologies if I added confusion. 

[jlafrenz]

Not much by way of direct experience... this thread caught my attention because I just replaced the tube in my Nova.

I find it interesting the specs for the Decco 2 call for a 6N1P, while the Nova has a 6922. My original, stock tube went bad, and I replaced it with a vintage 6DJ8. Major sonic improvement.

I have tube rolled every piece of tube gear I have bought and found improvement. Your thread was one that I had read and was really hoping that a different tube could tailor the sound of the Decco 2 to my liking. It seemed so strange to me that a 6DJ8 didn't work in my application, especially after reading your impressions of swapping the tube. I'm now at the point of trying to figure out what I want to do with the Decco 2 long term. Keep it or not.

[Mike Nomad]

I have tube rolled every piece of tube gear I have bought and found improvement. Your thread was one that I had read and was really hoping that a different tube could tailor the sound of the Decco 2 to my liking. It seemed so strange to me that a 6DJ8 didn't work in my application, especially after reading your impressions of swapping the tube. I'm now at the point of trying to figure out what I want to do with the Decco 2 long term. Keep it or not.

Looking at what Wayne1 said, it looks to me like you simply strayed a little too far in going with the 6DJ8: The 6DJ8 is much closer to a 6922 (the stock tube for my Nova) than a 6N1P (the stock tube for your Decco).

As I try to do a little math here... The tube I used as a replacement has a filament drawing 21.67% _more_ (ugh... I wonder if I need to sweat that...) than the original, while your replacement is drawing 39% _less_. I guess your replacement tube was being overdriven.

I think you'll get what you want sonically, if you go with another 6N1P, or (judging from my experience) something with a filament that draws more, not to exceed 21.67%.

[jlafrenz]

Thanks for all the info gentlemen. It makes sense now.

I did a quick search for 6N1P tubes and there wasn't much for choices and the ones that are available, I am not familiar with. Anyone have any recommendations for a replacement?

[rlee8394]

I believe that only one vendor made the 6N1P, Vostok factory I believe. Others, including myself, have replaced the 6N1P with 6CG7/6FQ7 with excellent results. It will work as a direct drop-in replacement.

Ron

[jlafrenz]

I believe that only one vendor made the 6N1P, Vostok factory I believe. Others, including myself, have replaced the 6N1P with 6CG7/6FQ7 with excellent results. It will work as a direct drop-in replacement.

Ron

I do see the Vostok ones, but assume that if they are the only ones making them then it would likely be the same tube that I have in the unit already. Is there a particular tube brand you would recommend of the 6CG7/6FQ7 variety?

[Steve]

I recently picked up a Decco 2 and decided to try a couple of different tubes in it to tailor it to my tastes. I see that 6N1P tube are in the same family of the 6DJ8 so I picked up a tube at a local shop to try out. As soon as I turned it on, there was lots of distortion and crackling so I shut it off to avoid any damage to the unit. The shop said they tested the tube, but I figured one may have slipped through. I have some other 6DJ8's laying around so I tried one of those and had the exact same issue. So now I am wondering if it is the tubes I am putting in it or the unit itself. What might be causing this or what am I overlooking?

Hi Jla,

With distortion, and crackling, as bad as you appear to indicate, I doubt that two tubes are bad. Is it one channel or two? I suggest  four areas to check.

1) Filter capacitor in the power supply becoming leaky and dropping B+ voltage. Check resistors connected to filter capacitor sections. If capacitor/resistors bad, recommended change all. Could also be just a resistor in the power supply.

2) Cathode resistor changed value, or possible cathode bypass
capacitor changing cathode bias.   

3) Plate resistor(s) has changed value. Unlikely both channels are bad at once unless a batch of resistors defective.

4) Lastly Grid resistor opened up. Very unlikely but possible.

Points one and two most likely the problem areas, with number 3 being quite unlikely. Check point 4 lastly.

Hope this helps. 

[JakeJ]

Good points, Steve.

There certainly are other things than tubes being the wrong specifications for the circuit.  If you continue to have problems even though trying tubes that are the correct ones then Steve's pointers for troubleshooting should be on your short list.

[Mike Nomad]

As I try to do a little math here... The tube I used as a replacement has a filament drawing 21.67% _more_ (ugh... I wonder if I need to sweat that...) than the original (...)

Since there seem to be a couple of knowledgeable TubeHeads on this thread, I'll obsess on the above a little more.

Since the makers of the amp won't let anybody in the US who isn't them look at the schematics, I'm making an assumption in the following...

Assuming the amperage to the tube socket is fixed, and with a specific tube in mind for use, are there any problems that should be expected? I'm guessing that under-driving the tube would simply increase its MTBF (?)

[JakeJ]

Typically an under driven tube does not fail quicker but in fact lasts longer than if it is driven normally, BUT... in many cases an under driven tube doesn't sound as good as it might in a circuit that is optimzed for that tube.  So if say the plate voltage were run at 40 to 80 volts less than the data sheet calls, and the grid and bias voltages follow normal application parameters (keeping anode and cathode currents under control as well) will help a tube run cooler, still be well optimized for the circuit, and operate for a longer period before needing replacement.

Does that make sense to you and help a bit?

[Mike Nomad]

Typically an under driven tube does not fail quicker but in fact lasts longer than if it is driven normally, BUT... in many cases an under driven tube doesn't sound as good as it might in a circuit that is optimzed for that tube.  So if say the plate voltage were run at 40 to 80 volts less than the data sheet calls, and the grid and bias voltages follow normal application parameters (keeping anode and cathode currents under control as well) will help a tube run cooler, still be well optimized for the circuit, and operate for a longer period before needing replacement.

Does that make sense to you and help a bit?

Hi Jake,

Thanks for the explanation. I get the gist of what you are saying. The proof, as I suspected, would be in the schematic. Signal Path Int'l is not hip to showing it (to people in the U.S.).

Under-powering the tube having a sonic impact was something I thought about briefly. The sonic improvement realized from replacing the junk-stock tube with my currently under-powered one is so good, I'm happy, at least for the next little while.

When I get the itch, I have an Amperex 6922 gold pin from 1977 that I haven't listened to yet.

Thanks again,

Mike