[Vinnie R.]

All,

Audiocircle member jrebman was very kind to send me 2 pairs of 6GM8 tubes (ECC86) to try with the Isabella in place of the 6DJ8/6922/7308 family.  A pair of NOS GE's from holland (with the A-frame getter), and a pair of Russian 6GM8s (unknown brand).

I actually never played with the 6GM8s with the Isabella before.  The 6GM8 is a low voltage tube (30V max for the plate voltage), so in most cases, you CANNOT use it in place of tube in the 6DJ8/6922/7308 family.  However, the Isabella's plate voltage is 24V and the 6GM8s share the same pin-out, and same 6.3V heaters / heater current draw - so I knew they should work.

This morning I tested an Isabella on the bench with the 6GM8s installed - worked fine!     One thing to note was that gain was a little lower with both pairs of tubes that jrebman donated compared to the stock JJ 6922's (approx. 0.1V less output at the 0dB gain setting on the Isabella, and approx 0.6V less output with the 12dB gain setting).  This is really not a big deal, but I wanted to mention this because you'll need to do the usual level-matching for accurate A/B comparisons. 

In the next day or two, I hope to carefully listen to these tubes and report back on how they sound.  For now, I justed wanted to start a thread about this and let everyone know that these do work with the Isabella!  If any Isabella owners have a pair of 6GM8s, give 'em a try and report your findings! 

Thanks again to jrebman for his generousity in donating some 6GM8s!

Vinnie

[jrebman]

Hi Vinnie,

My pleasure and I apologize for taking so long to finally get them to you.  I'm glad they didn't blow up the R&D lab at Red Wine Audio .  I'm going to be really interested to see what you think of the sonics as you get some time on them and time to listen as well.  One thing is that you'll probably never find a microphonic one, and they are very sturdily built and long-lived tubes, and I'd imagine even more so in the Isabella circuit.

Glad they're working out,

Jim

[Alwayswantmore]

Hi Vinnie,

My pleasure and I apologize for taking so long to finally get them to you.  I'm glad they didn't blow up the R&D lab at Red Wine Audio .  I'm going to be really interested to see what you think of the sonics as you get some time on them and time to listen as well.  One thing is that you'll probably never find a microphonic one, and they are very sturdily built and long-lived tubes, and I'd imagine even more so in the Isabella circuit.

Glad they're working out,

Jim

Hey Jim, can you please give us an idea for the going prices on these? Thanks, Kent

[wilsynet]

TubeWorld is not well known as a bargain, but they do have some in stock.

https://www.tubeworld.com/6e5.htm

Search for 6GM8 and you'll get:

3 pairs $80/pair) 6GM8=ECC86 Amperex Holland branded as Siemens NOS "O" getter halo in Siemens boxes around 1966 (recommended)
8 pairs $60/pair) 6GM8 Amperex Holland NOS 1970's A-Frame (sweet sound, quiet pairs)
2 pairs $60/pair) 6GM8=ECC86 Amperex Holland branded as Siemens NOS in Siemens boxes around 1970 A-Frame (recommended)

[BillB]

Note that other than the a-frame they are all identical built in Holland. I have a sleeve of GE, an Amperex and a Siemens and they are all the same.

Try a set of Reflektors (6n27p I believe they were), I am using 4 in my Aikido and I liked them a tad better than the Holland tubes. I only have 1 A-frame so I couldnt get an idea if it is better or not.

[Vinnie R.]

All,

I did make some time to listen to the 6GM8s that jrebman sent to me.

First, let me confirm that they work perfectly fine in the Isabella.  So if you have a pair (or thinking of trying a pair), they are
totally interchangeable in the Isabella (again, due to the lower plate voltage of the Isabella - but they are probably NOT compatible with 6DJ8/6922 tubes in other preamps if they run above 30V on the plates  ). 

As for the sound, keep in mind that I only spent an evening with them, so these are quick "initial impressions," used in the Isabella:

-- With both sets of 6GM8s that jrebman sent, one thing that stood out to me immediately is that they offer quite a bit more detail and energy the top end (compared to the stock JJs, and even compared quite a few of the NOS tubes that I've used).  If you are looking for more detail in your system, you might want to give these a try.  It is probably a lot less expensive than switching to all silver cabling.

The tonal balance of the NOS GE 6GM8s was shifted a little more to the top end.  Compared to the stock JJs, the bass was a little bit lighter, the midrange was more lean, and the top end was more detailed and lively.  "Float like a butterfly, sting like a bee."   Well, they don't "sting" because they are not strident, but you notice the change in presentation quickly enough!

The Russian 6GM8s (no brand was on the label - they only said "6GM8") offered some more bass weight and some more fullness in the mids compared to the GEs, but still not as much as the stock JJs.  The top end has similar characteristics to the GE.

For those who are looking for a less "tubey" sound (more like a good solid-state sound with some added dimensionality of tubes), definitely give the GE 6GM8s a try in your Isabella!

----

To conclude these initial impressions, I will say upfront that I preferred the stock JJ 6922 tubes to both of these.  I found the JJs had better tonal balance, a more "juicy" midrange (more tone, more density) and a sweeter top end (although these 6GM8s unraveled finer details and nuance, but at the expense adding more dryness to mids and a little less bass weight). 

The funny thing is that on the bench, the 6GM8s and the stock JJ 6922s both measure flat from 10Hz all the way past 100kHz on the o'scope, so this is another reason why you cannot simply rely on measurement - when you listen, the differences between the 6GM8s and the stock JJs is quite noticeable!

Finally, in your system (your electronics, speakers, room, and your taste in sound) - you might get different results and end up loving these 6GM8s.  I was very pleased to find that not only do they work fine in the Isabella, but that they offered a different presentation like this.  This gives the Isabella user more choices of tubes to try... the essence of tube rolling! 

If anyone else gives them a try, please post your findings here!

Best regards,

Vinnie

[jrebman]

Kent and all, first of all, those tube world prices seem absolutely ridiculous.  Most of the ones I have I bought in bulk for about $6 each, and most other places that have them typically sell them for $8 to $10 each, and matched pairs of Holland or West German made ones are in the $25 to $30 range.  They're getting harder to find and the sources where I got most of mine are sold out and don't expect any more in.

That said, some places like tubedepot.com and thetubestore.com may have them in singles.

I'll have to check to see if my new tube tester will work on these.

You should also know that any tube that says 6gm8 (other than Russian ones) and does not say made in Holland or West Germany is most likely a 6922 that has been relabeled.

There really is very little difference (other than the a frame types) between the various brands that say made in Holland or West Germany, so a GE is probably exactly the same thing as an Amperex.  Valvo does seem to be the exception and is again, most likely not a true 6gm8/ecc86.

Vinnie, thanks for the sonic impressions of the tubes, It'll be interesting to hear if and how that changes as they get some time on them.  The handful of folks I know who have 6gm8 based preamps love them.  At least I'm glad they give Isabella users another flavor to roll with.

-- Jim

[BillB]

The Russians are most likely Reflektor, they are the only ones I have seen.

Here is a pic of my motley crew, minus the Amperex, which is identical to the GE and other Siemens anyways...it appears to be MIA right now.

[Vinnie R.]

Hi BillB,

Thanks for your post and the picture.

Just from my memory, I think the Russian one that jrebman gave me looks like the one on the left, and the GE looks like the GE shown
in the pick (yes, Made in Holland).

So are you guys saying that the ones Made in Holland (offered by the different brands like GE, Siemens, Amperex) are essentially the same tube, and perhaps came from the same production plant - or are there clear sonic differences?

Vinnie, thanks for the sonic impressions of the tubes, It'll be interesting to hear if and how that changes as they get some time on them.  The handful of folks I know who have 6gm8 based preamps love them.  At least I'm glad they give Isabella users another flavor to roll with.

Hi Jim,

I'll post a follow-up when I get more time to listen and let 'em cook for a while..

Thanks again,

Vinnie

[jrebman]

I just wanted to update folks on 6gm8 pricing.  Apparently the relative scarcity of these tubes has made the prices go up quite a bit in just the last year or so.  It looks now like $60 - $70 for a matched pair of holland made, A-frame types is pretty typical.

Sorry, but I still have no further information on where to find them nowadays, but I'd just suggest keeping an eye out on ebay if you're interested, and also check with the folks who bring in more of the russian tubes for the 6n27p types.

As they were pretty much exclusively made in Europe, that's where they might be easier to find, and of course if you find any old car radios from the 50s and 60s, look in them for pulls as the tubes are often still going to be good.

Hope this helps,

Jim
P.S. -- For those who have been asking, for now I'm going to hold on to my stock in case the bug for a project or two pops up.

[Vinnie R.]

Hi Jim,

Thanks for the follow-up.

Since my last post, I've listened to these some more and pretty much what I post above stands (again - it's just my opinion of them in my system).

I think they are great for those looking to obtain more detail.  I can see that in some systems and some listeners, they might be a preferred tube.

We'll add them to the "accepted tubes that work with the Isabella" list! 

Thanks again,

Vinnie

[Fork]

I recently found a pair of these on Ebay (Telefunken/Valvo) for $40.  My interest was in finding a tube that would give my Druid/Red Wine combo a higher frequency center (I find the combination to have a balance that's focused on the low end), with more detail and holography. 

The tube construction was identical to my 7308, except not having gold pins and having more girth around the bottle.  I'm sending the tubes back because one arrived DOA.  I was able to listen with one channel and my conclusions were similar to Vinnie's, except for them adding detail. 

I did hear a lot more upper-mid and low-treble energy and the low bass was rolled off.  I did not agree, with this model, that it enhanced the detail; I found the opposite to be true.  I found that the upper frequencies had much more thrust and kind of steam rolled the detail and nuance out of the sound.  I can't say if I might have favored another brand, but I would never have used these tubes in this system.

Still, I remain interested in hearing about more choices and listening tests from Vinnie, particularly on tubes that aren't expensive.

[Vinnie R.]

Hi Fork,

I'm sending the tubes back because one arrived DOA.  I was able to listen with one channel and my conclusions were similar to Vinnie's, except for them adding detail. 

I never tried the Telefunken/Valvo 6GM8s.  Sounds like you were listening with only one channel (Too bad one came DOA).

If you ever get a chance to try another pair of 6GM8s with your Isabella, I look forward to hearing your impressions.

Lately I've been listening to the Amperex 7308s ("USN-CEP", made in USA, gold pins) and really like these a lot.  I purchased from from Steve at Northlake Audio, but he is all sold out.  He had over 20 pair and they all sold quickly. 

When I get some free time, I hope to try other tubes and post my findings.

Best regards,

Vinnie

[Fork]

I'm listening to the Amperex 7308s right now a 30.2/Isabella w/ Zu Druids.  After spending more time with the original JJ tubes, to compare, it seems to me that these two are similar in many respects.  The 7308s are said to sound more light and spacious and I agree.  To my ears the effect is from lighter, more snappy bass in the 7308.  The JJs have sweet treble with good articulation, but their bass gives them a bigger sound that's not as airy.  I might prefer the JJs if my speakers had more room to breath.  In my current setup I prefer the 7308, but that preference is slight.