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In Reply to: HP branded Amperex 6DJ8/ ECC88 tubes - Help! posted by Bibi on September 22, 2004 at 02:16:01:
I have many of these tubes labeled HP as well as other brands.The A-frame is generally well regarded. I don't like this tube. To my ears, in my set-up, it is bright and thin, if it is open plate construction.
For my money, the Amperex Bugle Boy/closed plate is the tube to have for 6DJ8. Warm, dimensional, great resolution and extension overall. In the 6DJ8 family, I don't think there is really a better tube.
To my ears, what I refer to as the 'closed' plate construction are the better sounding tubes overall versus the 'open' plate type no matter the getter type. With open plates you can see the internal, i.e. grid and heater. With closed plates you cannot. Closed plate where produced earlier. Generally, you will see A-frame getters on later production open plate type tubes. Earlier production close plate generally had halo or D type getters. Good sounding tubes with both types of plate construction, but overall the closed plate version are better.
That being said, I do have (4) HP labeled Philips/Holland tubes from the early 70s that have closed plate construction and A-frame getters. Very nice sounding tubes. Getter construction does impact sonic performance, but plate type has a far greater impact IMO.
I would not get too worried about actual production dates. With the Bugle Boys for example, they sounded great no matter the date. I suppose the earlier versions are better, but it would be minor at best. I have Bugle Boys from the late 50s to late 70s when the production line moved to Japan. Still a killer tube no matter the date!
Gives these tubes a listen. They may sound great in your set-up. There are plenty of folks around here that like this tube and that is all the really matters.
Follow Ups:
All of the HP 6DJ8's that I have are coded as "B" for Blackburn, UK, but are also date coded as 70's tubes with A frame and "closed" plates.
Yes. I have this tube from the early 70s labeled HP. I can't recall which plant produced the tube. I will check to see if they came from the UK or Holland.Most of the HPs I have are actually Holland produced Bugle Boy types from the mid-60s, or the open plate versions from the late 60s also produced in Holland.
I have a number of the HP labeled tubes that have 78-34 in white as an HP date code and are marked in white Made in USA but with B6L4 in the second row of the etched code.I suspect these were manufactured in 1974 in Blackburn, and perhaps the Blackburn plant continued to make the "closed plate" tubes long after the Harleen plant went to the open plate design.
I also noticed that al of the Harleen manufactured A frame 6DJ8's I have are indeed open plate.
Anyone know how the Blackburn made 6DJ8 sounds?
All these variations, plants, etc., can get confusing!I have many Mullard branded 6DJ8 produced in the UK that are physically identical to the Bugle Boy produced in Holland. These are mid-60s productions. To my ears they sound virtually identical. Any variations in sound are probably Audiophile Induced Delusion on my part than any real sonic difference.
Is there a site with pix of open vs. closed plate and/or getter format? We have lots of old HP and Tek scopes here. ;-)
I too have a collection of old Tek scopes for parts.I'll post some pictures soon and then everybody can take their time identifying them and listing the various frame, plate, and getter strictures etc.
I have never seen a site with pics of the various plate types.The names I give for the plate structure is of my own choosing. It seemed logical to me. Later production Philips 6DJ8 had the 'open' plate structure. The plate halves do not mate and a small bit of metal is spot welded on the plate halves in the area between the top and bottom mica spacers. You can clearly see the grid and heater. I think Philips started using this plate type in the late 60s. I have never seen one of these with an earlier production date.
With 'closed' plate, earlier production, the plate halves mate so you cannot see the internals of the tube and the connection between the plate halves is made above the top mica spacer. While I have a few examples of this type of Philips tube from the early 70s, generally later production Philips/Holland no longer used this plate structure. Perhaps these were produced much earlier and date coded later once sold to HP. Just a guess on my part.
All of the Japanese produced tubes I have from the 60s and 70s produced on Philips tooling use the closed plate. I also note the new JJ produced tube use the closed plate. To my ears, the closed versions are generally better.
mt
Thanks everyone for the very useful insight'.
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