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Follow-up on my matching tube post below

73.114.133.239
Posted on June 30, 2017 at 16:02:34
JoshT
Audiophile

Posts: 6622
Location: Eastern Massachusetts
Joined: July 4, 2000
 Thanks for all the input on my question below about tube origin and matching.

I have finally been able to open up the Rogue RP-5 preamp and remove the tubes for inspection, and here is what I found.

Here is a picture of one pair.
One tube says Mullard, Made in [hard to read but looks like Great Britain] and has the following etched numbers on the bottom: K6 B8E
The other tube says Amperex [with Bugle boy emblem] 930, Made in Great Britain, with etched number on the bottom: K6 B8K





Here is a picture of the other pair.
One tube says Heath, Mullard, [country of origin wiped off], has etched side numbers 845 1022
and etched bottom numbers B8E (nothing else noticeable)
The other tube says Mullard, Made in Great Brittain, has etched side numbers 841 1022 and etched bottom numbers K6 B8C.




I have been unable to decode the etched numbers based on the guide inmate Sondek kindly provided, but given the fact that the construction of each looks identical to me and that they all appear to have similar codes and are all made in GB, I assume it would be reasonable to assume they are both matched pairs as represented by the seller and that no mistake was made in putting them together.

I would be interested in any comments on these tubes. They sound great to me, except I think I might be hearing some microphonics from one channel (a slight ringing sound following higher note piano strikes), though I'm going to check on another system. Also, unfortunately, I am getting some static sound occasionally through the headphone amp, which may or may not be tube related (Rogue said it could be an opamp instead). I have checked the headphones on my Oppo and they are fine, so it's in the headphone circuit. So, I have the stock JJ tubes in now and will see if the static continues with the headphones.
___
"If you are the owner of a new stereophonic system, this record will play with even more brilliant true-to-life fidelity. In short, you can purchase this record with no fear of its becoming obsolete in the future."

 

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RE: Follow-up on my matching tube post below, posted on July 1, 2017 at 07:42:23
ksk
Audiophile

Posts: 86
Joined: July 29, 2010
 k6 (lowercase k) is a ECC82 (12AU7)

B is Mullard Blackburn factory
8 is 1968 (or 1958)
C is March

 

Thanks!, posted on July 1, 2017 at 12:33:31
JoshT
Audiophile

Posts: 6622
Location: Eastern Massachusetts
Joined: July 4, 2000
 Much obliged.

Unfortunately at least one seems to be bad. With the stock JJs back in the static and slight ringing sound is gone.
___
"If you are the owner of a new stereophonic system, this record will play with even more brilliant true-to-life fidelity. In short, you can purchase this record with no fear of its becoming obsolete in the future."

 

If you are experiencing micro phonics with the 12au7(s) used in..., posted on July 1, 2017 at 13:36:26
DeKay
 the gain stage of the preamp (it feeds the headphone stage) you could try later production short plate 12au7's from the Mullard Blackburn plant as they tend to stay quiet if properly tested/screened.

They are usually under $100/matched pair.

The ones I use are from the late 60's/early 70's and they are typically branded with the Amperex Orange World/Globe label.

Brente Jesse sells them, for certain, but other tube vendors may have them as well.

In my preamp/system they are similar in sound to the older long plate versions.

 

RE: Thanks!, posted on July 1, 2017 at 19:06:34
Sondek
Audiophile

Posts: 9626
Location: Fort Worth
Joined: May 17, 2000
Contributor
  Since: April 5, 2002
 The static could be dirty or loose pin connection. A sewing machine needle works pretty well for retensioning socket connections. The JJ pins might be just a smidge fatter and make a better connection.

 

The Mullards were in very snuggly, but . . ., posted on July 2, 2017 at 12:47:46
JoshT
Audiophile

Posts: 6622
Location: Eastern Massachusetts
Joined: July 4, 2000
 It's possible one or more of the pins were dirty. They were quite hard to remove. Had to hold the sockets down because it seemed like they would pull out of the PCB otherwise. Actually, the JJs slid in a bit easier though they're snug too..

I'm going to get some Deoxit for the tube pins though. The preamp is brand new so the sockets should be clean I'd think.

Now that I believe the problem was clearly with tubes (since I've had no issues with the JJs), my next step after the Deoxit will be to put the Mullards back in, but swap the gain stage pair for the driver pair (front pair with rear pair) and see if the static returns or if everything is OK as it is with the JJs. In that case I'll replace the bad pair (hopefully covered by warranty, but the timing is tight).

The JJs don't sound bad at all actually. The major difference is that the Mullards have better bass (both seemingly deeper and definitely tighter more defined). The midrange and highs sound about the same to me actually.
___
"If you are the owner of a new stereophonic system, this record will play with even more brilliant true-to-life fidelity. In short, you can purchase this record with no fear of its becoming obsolete in the future."

 

RE: If you are experiencing micro phonics with the 12au7(s) used in..., posted on July 2, 2017 at 12:49:23
JoshT
Audiophile

Posts: 6622
Location: Eastern Massachusetts
Joined: July 4, 2000
 Thanks for the suggestion. I'll experiment and keep that in mind. Are mine the long plates (based on the pictures)? Mine were all made in 1958 according to Brett Jesse and also the code numbers etched into the glass at the bottoms.
___
"If you are the owner of a new stereophonic system, this record will play with even more brilliant true-to-life fidelity. In short, you can purchase this record with no fear of its becoming obsolete in the future."

 

Yes, your pics are of LP's..., posted on July 2, 2017 at 17:02:59
DeKay
 My personal taste (in my setup) goes to those and the much later production SP mentioned.

I have quite a few of the Blackburn Ecc82's produced in the interim between the "Two" which are labelled standard Mullard as well as IEC Mullard & Daystrom (sp?) and I much prefer the expensive LP's and the less inexpensive later SP versions.

However, considering excessive noise the later SP's, properly screened would be a fine alternative, IMO.

I've read about the "special" current production 12au7's, but as they cost more than I've ever paid for old production (including LP's) I've yet to try any.

If you click on my system you will see that the electronics are separated from the listening room by a wall, but even with this I've experienced a few problems with micro phonic tubes.

 

And... a PS to my post below..., posted on July 2, 2017 at 17:14:54
DeKay
 As you have 4 of the LP's and assuming that only 2 of them are used for gain you could try the noisy tube in a non gain position (which would get you up and rolling right away assuming the other 3 are much less noisy).

Ask your dealer about which positions/sockets do what within the preamp and then swap the tubes accordingly.

If this works then you have plenty of time to research backup tubes.

 

Yeah, it was as you said, a bad tube in the gain stage, posted on July 2, 2017 at 22:04:05
JoshT
Audiophile

Posts: 6622
Location: Eastern Massachusetts
Joined: July 4, 2000
 I figured as much when inserting the JJs stopped the static sound through the headphones and what seemed like microphonics.

I just reversed the matched pairs, so the pair that was in the diver sockets are now in the gain sockets and vice versa. The preamp sounds fantastic. No static through the headphones and a wonderful, rich sound with strong bass.

I bought the tubes through my local dealer, who sourced them from Brett Jesse, and it's been just under 30 days since I bought them (but maybe more since my dealer did) so I'll call my dealer on Wednesday and see what he/Jesse can do regarding the bad tube.

Sounds great though. Now I have a better understanding of the limitations to the JJs. Though they have a lovely tubey sound in the Rogue, the highs are a tad bright and the bass a bit flabby. The Mullards sound more neutral from top to bottom. Less bright but more defined treble and more extended and defined bass. At least that's how I hear it.
___
"If you are the owner of a new stereophonic system, this record will play with even more brilliant true-to-life fidelity. In short, you can purchase this record with no fear of its becoming obsolete in the future."

 

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