[gibosi]

Made in Great Britain GE 6HM5/6HA5 followup:
 
GE Made in Great Britain by GE. Date unknown.
 

 
GE Made in Great Britain by Mullard/Blackburn, 1970 (B0F1)
 

 
First, both of these are excellent tubes on par with my recent favorites, GE 6AV6, Raytheon 6BE6W and Tung Sol 6DT6, with punchy bass with good articulation and detail, crystal clear and clean highs, and a wide and deep stage. The primary difference between the two GEs is warmth. As one might predict, the Blackburn-made GEs add just a bit of warmth to the upper bass and mid range. Interestingly, the difference in warmth between these two GEs is quite subtle and not as noticeable as between the Mullard/Blackburn and GE 6AV6.
 
Those of you who have been thinking about trying some triodes, but feeling a bit squeamish about the need to amputate and mutilate perfectly good tubes lol, I encourage you to get a pair of these GE 6HM5/6HA5. They require no strapping or mutilation of any kind. Simply set up the LD for EF95 tubes, plug them in and play.
 
Also, I have seen Sylvania 6HM5/6HA5 on eBay that appear to have the same internal construction as the GE-made tubes. And further, I recommend you avoid the short, squat 6HM5/6HA5 tubes. 
 
Recommended.

 

[kvtaco17]

  Made in Great Britain GE 6HM5/6HA5 followup:
 
GE Made in Great Britain by GE. Date unknown.
 

 
GE Made in Great Britain by Mullard/Blackburn, 1970 (B0F1)
 

 
First, both of these are excellent tubes on par with my recent favorites, GE 6AV6, Raytheon 6BE6W and Tung Sol 6DT6, with punchy bass with good articulation and detail, crystal clear and clean highs, and a wide and deep stage. The primary difference between the two GEs is warmth. As one might predict, the Blackburn-made GEs add just a bit of warmth to the upper bass and mid range. Interestingly, the difference in warmth between these two GEs is quite subtle and not as noticeable as between the Mullard/Blackburn and GE 6AV6.
 
Those of you who have been thinking about trying some triodes, but feeling a bit squeamish about the need to amputate and mutilate perfectly good tubes lol, I encourage you to get a pair of these GE 6HM5/6HA5. They require no strapping or mutilation of any kind. Simply set up the LD for EF95 tubes, plug them in and play.
 
Also, I have seen Sylvania 6HM5/6HA5 on eBay that appear to have the same internal construction as the GE-made tubes. And further, I recommend you avoid the short, squat 6HM5/6HA5 tubes. 
 
Recommended.

How would you compare these VS the 6DT6?

 

[gibosi]

  How would you compare these VS the 6DT6?

 
I haven't listened to the RCA 6DT6 in awhile (which I understand is your current favorite), so will try to find some time to do a quick comparison in the next day or so.
 
Cheers

 

[kvtaco17]

   
I haven't listened to the RCA 6DT6 in awhile (which I understand is your current favorite), so will try to find some time to do a quick comparison in the next day or so.
 
Cheers

Thank you much! The RCA's and Sylvania's are tied for my favorite lol

 

[Edgard Varese]

  any strap recommendations for the RCA 6DT6A's? currently running ef95 no strap but bass a bit boomy

 
 
The switch to EF92 made mine sound much better.  They were a bit sibiliant last night though, but I think it might just have been my pre-existing headache. 

 

[Acapella11]

   
EF95 6/7 = more forward and much more controlled bass then unstrapped
"     " 1/7 = More bass the above, but much more controlled then stock... more laid back and airy
"     " 2/7 = more similar to 1/7 except less bass impact and slightly more forward.
 
All good, just depends on what you like.

 
Agreed kvatco17!
 
Just received mine today (GE 6DT6A). Which setting do you use Mordy?
Unstrapped bass is not my blues, 2/7 too forward. I am between 6/7 and 1/7, both work well in different ways.
 

  The switch to EF92 made mine sound much better.  They were a bit sibiliant last night though, but I think it might just have been my pre-existing headache. 

 
6/7 and 2/7 can be a bit sibilant depending on your music but also nicely energetic. With 1/7 sibilant sounds are reduced.
 
Also got a pair 10M 6AV6.
 
Both pairs sound very nice and also very different.

 

[MIKELAP]

This is  Montreal band BEAST very good tune 
DARK EYES  

 

[gibosi]

  How would you compare these VS the 6DT6?

 
OK... A quick comparison of the GE-made 6HM5/6HA5 and the RCA 6DT6. (Sorry, but I do not have a Sylvania 6DT6. And I think from now on, I will shorten 6HM5/6HA5 to just 6HM5.)
 
As these are both very good tubes, the differences between them are quite subtle. And since you like the RCA 6DT6, I am quite sure you would also like the GE 6HM5.
 
The stage on both of these is nice and wide, but the 6HM5 is a bit more 3D. Sounds off in the distance actually sound like they are indeed farther away.
 
The other primary difference boils down to "house sound." In my experience, the RCA house sound is typically a warm sound with good bass presence. The GE house sound does not have the same degree of added warmth, and at least to my ears, seems a bit more natural. Thus, vocals and upper bass on the RCA 6DT6 are warm and full, whereas, on the GEs, vocals, while still sweet, seem cleaner and more natural to me. And similarly, the bass on the GEs also seems to be a tad bit cleaner, with slightly better detail and articulation. But again, I think these differences are quite subtle, and I find both tubes to be very good. However, my 1958 GE 6AV6s (and clones) are still my go-to tubes.

 

[Edgard Varese]

   
OK... A quick comparison of the GE-made 6HM5/6HA5 and the RCA 6DT6. (Sorry, but I do not have a Sylvania 6DT6. And I think from now on, I will shorten 6HM5/6HA5 to just 6HM5.)
 
As these are both very good tubes, the differences between them are quite subtle. And since you like the RCA 6DT6, I am quite sure you would also like the GE 6HM5.
 
The stage on both of these is nice and wide, but the 6HM5 is a bit more 3D. Sounds off in the distance actually sound like they are indeed farther away.
 
The other primary difference boils down to "house sound." In my experience, the RCA house sound is typically a warm sound with good bass presence. The GE house sound does not have the same degree of added warmth, and at least to my ears, seems a bit more natural. Thus, vocals and upper bass on the RCA 6DT6 are warm and full, whereas, on the GEs, vocals, while still sweet, seem cleaner and more natural to me. And similarly, the bass on the GEs also seems to be a tad bit cleaner, with slightly better detail and articulation. But again, I think these differences are quite subtle, and I find both tubes to be very good. However, my 1958 GE 6AV6s (and clones) are still my go-to tubes.

 
 
It's interesting that you mention this as I have been thinking about trying a tube that is a bit more "holographic" seeming.  I should get a couple of the 6HM5s...

 

[MIKELAP]

Like you say gibosi those 6AV6 are hard to beet was listening to some RCA 6DT6A still prefer the 6AV6 in this case G.E. JAN 6AV6 they sound cleaner.

 

[mordy]

Hi A11,
 
"Just received mine today (GE 6DT6A). Which setting do you use Mordy?"
 
Started out with the EF95 1/7, but now I use EF92 NS, and I am happy with this ( but I liked the 1/7 setting as well) . My 6DTA6 tubes in use at this time are Japanese made, either by Hitachi or Toshiba and perhaps they come from the same factory as the (demystified?) Siemens Foreign and Haltron tubes.
 
I will try to post pictures later of these three tubes, but right now I am away from home for a few days.
 
PS: IMHO the 6DT6 tubes require 30-50 hours burn in to enter their prime.

 

[TrollDragon]

Well the switches are installed, one for each side to do 1-7 / NS / 2-7 and for me this way is quite a lot easier than strapping in the socket.

 
Nothing is ever done without incident though...
With everything put back together, I popped in the 6DT6A's set the switches for the 1-7 strap and turned on the LD.
Played Dire Straits "Brothers In Arms" 20th Anniversary Edition in 24/96, "Money for Nothing" will raise goosebumps on your goosebumps!
 
So I figured lets try 2-7, I shut off the LD and flipped the switches. One of the 6DT6A's looked a little crooked, I straightened it and turned on the LD. Well all I was presented with was HUM, independent of the volume control this HUM was there and changed pitch when you brought your hand near the chassis.
 
Well didn't the panic set in, the switches are bad, the switch wire is picking up HUM, these new tubes are bad? So I powered off, changed to the 6CS6's and upon turning the power back on the HUM was back... Panic turning into annoyance at wrecking my LD and I am going to have to take it apart to see what fried, but there was no smell...
 
Anyway to make a long story short the top front right screw that holds the circuit board to the chassis was loose, this screw provides the ground between the chassis and the board. I had put it in first without tightening it so I could line up the other standoffs with the holes.
 
If you ever have the board out of the LD, make sure the top front right screw is tight upon reassembly. Once I screwed it down and powered up the LD again, the HUM was completely gone and let me tell you what a huge relief that was.

 

[Audiofanboy]

  Well the switches are installed, one for each side to do 1-7 / NS / 2-7 and for me this way is quite a lot easier than strapping in the socket.
 
Nothing is ever done without incident though...
With everything put back together, I popped in the 6DT6A's set the switches for the 1-7 strap and turned on the LD.
Played Dire Straits "Brothers In Arms" 20th Anniversary Edition in 24/96, "Money for Nothing" will raise goosebumps on your goosebumps!
 
So I figured lets try 2-7, I shut off the LD and flipped the switches. One of the 6DT6A's looked a little crooked, I straightened it and turned on the LD. Well all I was presented with was HUM, independent of the volume control this HUM was there and changed pitch when you brought your hand near the chassis.
 
Well didn't the panic set in, the switches are bad, the switch wire is picking up HUM, these new tubes are bad? So I powered off, changed to the 6CS6's and upon turning the power back on the HUM was back... Panic turning into annoyance at wrecking my LD and I am going to have to take it apart to see what fried, but there was no smell...
 
Anyway to make a long story short the top front right screw that holds the circuit board to the chassis was loose, this screw provides the ground between the chassis and the board. I had put it in first without tightening it so I could line up the other standoffs with the holes.
 
If you ever have the board out of the LD, make sure the top front right screw is tight upon reassembly. Once I screwed it down and powered up the LD again, the HUM was completely gone and let me tell you what a huge relief that was.

 
Speaking of grounding, my next experiment involves using a double triode for each -single- channel, meaning that only one triode section would be used, with the other section just "floating" but heated. I know that can't be very good over the long term...
 
So, I believe I should be grounding that unused triode section to avoid problems. Do you have any suggestions as to how I could do that easily (like wire those pins straight to the chassis or something)?

 

[Audiofanboy]

Ok, more tube silliness for anyone who's still interested. This time, no electrical theory, all DIYP (do it yourself poorly) practice!
 
I'd said I got a single 12AT7 tube to work for both channels (two triodes in the tube, one used per channel, ugly and risky mod), and that my next attempt would be to -cleanly- adapt a 6DJ8/ECC88 (thereafter ECC88, since that's what I used) to each channel, therefore only running one triode out the two in each tube. Not particularly hard or risky compared to my previous "mod" definitely prettier, less impressive, but more logical for long term use.
 
I got my EI "made in Yugoslavia" ECC88 tubes in the mail 24h after ordering them (for once, they shipped from close to me, so I didn't have to wait the usual whole week). Why wait any longer to test them? So, I immediately processed to adapt some socket adapters to an idea that had popped into my head yesterday, looking at tube datasheets, and mapping out which ECC88 pin would have to go to which B7G socket hole to use either triode 1 or triode 2 of the tube.
 
But first off, how funny/interesting/odd is it to have driver tubes from (ex-)Yugoslavia lol? Apologies for anyone from the Balkans region, but when I think of current Serbia, my first thought isn't about high-tech gear... Still, those are very fine tubes, evidently made on Philips factory lines, but in the EI Nis factory in ex-Yugoslavia. Date coded with a 9, meaning made in 1979 or 1989, before or after is unlikely (I don't believe they had Philips lines in '69, the country was kind of at war by '92, and I think those "A-frame" Philips getters were from later times, i.e., not the 50's or 60's). These are supposed to basically be Philips copies with similar high quality sound, but slightly lesser craftsmanship. They look solid at any rate!
 
When I mapped out how to use either triode in those tubes on our sockets, I realized that there was a way we could just fit these tubes in -an adapter not the native sockets- with very little modification.
 
Using ECC88 triode 2 meant mapping (ECC88 to 6AK5):
- pin 1 to pin 5
- pin 2 to pin 1
- pin 3 to pin 2
- pin 4 to pin 3 (or 4)
- pin 5 to pin 4 (or 3)
 
If you look at your socket holes, you'd quickly see that this would require a major adapter with wires between pins far apart; not easy.
 
On the other hand, mapping triode 1:
- pin 4 to pin 3 (or 4)
- pin 5 to pin 4 (or 3)
- pin 6 to pin 5
- pin 7 to pin 1
- pin 8 to pin 2
 
OK, so the pattern doesn't immediately strike you as obvious, I get it. But look at it this way: for pure triode use, pins/holes 6 and 7 don't serve any purpose in our amps (nothing needs to go to those holes at the socket level), so as long as socket hole 6 and 7 stay empty, you can use pins 6 and 7 on an adapter to do whatever you want. So, let's map those pins again, shall we:
- pin 4 to pin 3 (or 4)
- pin 5 to pin 4 (or 3)
- pin 6 to pin 5
- pin 7 to pin 6 (attached to pin 1)
- pin 8 to pin 7 (attached to pin 2)
 
Can you see where I'm going with this? Essentially, I realized that you can plug the five relevant pins of a ECC88 in a sequence of five consecutive holes on a 7-pin adapter; provided that you disconnect pins 6 and 7, and reroute pin 6 to pin 1, and pin 7 to pin 2.
 
And that's what I did, basically. I opened up a pair of my 7-pin adapters/savers, bent pins 6 and 7 inside the adapter (the pin are like 5cm long inside, so bending them allows the pins to not poke out of the adapter, and allows them to get close to the pins they need to be connected to), and soldered pin 6 to pin 1, and pin 7 to pin 2. Easy.
 
If you just couldn't be bothered or hate soldering, you could just get a pair of adapters, chop off pins 6 and 7, and manually strap pin 6 to 1 and 7 to 2 with the usual wire mod.
 
Next, with those adapters prepped up, you just have to manhandle the ECC88 tubes to fit in those 5 relevant pins in the 5 consecutive relevant holes (which would probably require you to bend the four left over pins on the tube, unless you have really small adapters). Look at the pics in full size if you want to get a better picture of what I mean.
 
And this is what you get; not too bad I'd say? Definitely prettier than the floating 12AT7 mod!
 

 

 

 
As per usual, it worked like a charm, even on the first try! Listening to the amp for a few minutes tells me that these are fine tubes, but I'll allow myself a few hours of burn-in before I give impressions. The purpose of this mod was to show that ECC88 type tubes can be made to work in each channel and not look too ugly; and I think that's goal's been reached!
 
Anybody else interested in joining me in double triode land lol?
 
Now, I just need to solve the floating triode issue (ground the heated yet unused triode)...

 

[TrollDragon]

   
Speaking of grounding, my next experiment involves using a double triode for each -single- channel, meaning that only one triode section would be used, with the other section just "floating" but heated. I know that can't be very good over the long term...
 
So, I believe I should be grounding that unused triode section to avoid problems. Do you have any suggestions as to how I could do that easily (like wire those pins straight to the chassis or something)?

I asked that question over at "I <3 Tube Amps" and got my arse chewed on hard by the pros there... 
Lucky to make it out of there unscathed, but I did manage to get some info from the guru's while running away in sheer terror. 

 
Two of them suggested to run both halves of the tube in parallel as opposed to floating or grounded.
 
Quote: I <3 Tube Amps

But IN GENERAL when paralleling triodes, the plate resistors, cathode resistors and grid stoppers get halved, an any cathode bypass caps get doubled.
So it might just not be feasible with out amp modifications...

 
Ponder it over and see what you think...