Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: mresistor on September 25, 2015, 05:41:07 pm
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here is a 5F1 Champ what is the power tube anyone know ?
(https://scontent-sea1-1.xx.fbcdn.net/hphotos-xpt1/t31.0-8/12045286_10153686040309743_6118449537555310227_o.jpg)
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I don't recall ever seeing a small base 6V6.
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6V6, I would guess. Absolutely, they were made with "coin" bases for some time. I mean, RCA definitely and GE (I think) made 6V6 tubes with coin bases. I think they were less popular because only the "top hold-down" type of tube retainer worked...the Fender claw and Birtcher over-center type tube retainers would not work because they clamped on to the octal base which was no longer there with that type tube.
Plus...the coin type base kind of came out in the 70's, I think, when a lot of stuff of all categories kind of became junky. I believe these style tubes are sort of associated with that era and people tend not to like them. I have no opinion as to whether they are better or worse than the "normal" style, I have only encountered one example, in a Champ I got in a trade and put in storage for 25 years. It worked fine, but that's indicative of nothing.
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6V6, I would guess. Absolutely, they were made with "coin" bases for some time. I mean, RCA definitely and GE (I think) made 6V6 tubes with coin bases.
Agree, I've seen 6V6's with the 'coin base'. I think, no I'm sure I have a pair made by Westinghouse that have that base.
I'll dig them out and post a pic. :icon_biggrin:
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Wow I didn't know they made 6V6 coin base. I also read they aren't the greatest tubes. Willabe I found a pic of a pair of them.
I know i'd seen some Russian tubes with coin base ( I thought) ... but all these years I think I've only seen or had one . So these
coin bases where for "cost savings" ?
(http://tctubes.com/images/products/detail/932_SYL_7591_PR_800.JPG)
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Now I know where I'd seen these. I have a Sovtek 6L6WGC that is coin base..
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So these coin bases where for "cost savings" ?
I think so. At least they look cheap. The only coin base tubes I've ever had were 7591s in an Ampeg Gemini II. And I currently have a new production pair of 7591s in a Hammond AO-63. Good sounding tubes but they sure look fragile. I'm always afraid I'll break the base when inserting them into a socket.
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Probably one of those things where some brilliant engineer thought "Wow, better heat dissipation and cheaper mfg cost, hurray for me!"
At the time they came out, tubes were going to be dinosaurs anyway, so who cared whether the idea was actually a good idea all things considered?
Again, I have zero reason to believe or suspect the interior of the tube changed in any way for better or worse, but they are obviously not happy choices for upside-use in Fenders, etc; In a stereo, who would care?
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The 7591s ran upside down in my Ampeg with no retainers. Never had one to drop out. In fact, the pins were a very tight fit to the socket. Same with the new production. So tight I fear I'll accidently break a tube while inserting/removing one of these days.
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those pins do look a little fat.. ;-)
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Agree, I've seen 6V6's with the 'coin base'. I think, no I'm sure I have a pair made by Westinghouse that have that base.
I have a Fender branded 6V6 with a coin base in my 1970s Silverface Vibro Champ. I am guessing it was the original stock power tube. No other markings or etchings on it to give it away.
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> for "cost savings" ?
Perhaps. It may really be better.
Look at a miniature tube (12AX7). Fairly fat leads come through a thick glass bottom button.
Bust-open the base of a dud conventional Octal tube. The leads are very thin, long, and must be threaded to and soldered into pins on a separate glued-on base.
The reason is that it is hard to get a long-lasting vacuum seal metal-to-glass, especially over a wide range of temperatures. Glass and metal expand at different rates, and the seal wants to crack. Historically, smaller leads reduce the problem. However small leads are near useless for carrying heat out of the electrodes. For several reasons, larger leads became practical as the Miniature tubes were developed. This allows a short fat connection. It also allows the lead to be the pin, saving threading and added parts. The instigation may have been low loss at very high (radio) frequency. But a fair amount of heat can be carried out the same way. And once debugged it was somewhat cheaper.
Conventional Octals were in decline. After the first decade of Tube TV, the Octal-size jobs went to large tubes on Miniature-type bases (but larger), like we find in a few Bogens. Since the old Octal designs and machines were working well, the few Octals still in production stuck with the old ways.
But by the 1970s the Octal machines may have been getting tired, or being sold-off to Hungary and other odd corners. And the total tube production in each hanging-on factory may not have justified *two* base systems with different machines and different materials to stock.
I think the coin-cell Octal is a giant Miniature, plus an adapter to fit Octal sockets. Note the stiff leads come out in the right places. No threading thin leads into the right pins, it just drops in.
The threading of Octal leads to pins may parallel the early IC chip process, where the pads on the dies had to be stitched to the pins on the package by hand. Once the die production got good, hand-stitching the die leads became a major cost and unreliability problem for the industry. One approach was leg-less packages, where the die pads were grown larger and soldered direct to PCB (an early SMD). This that and another, the cost of terminating an IC die dropped from several dollars to several cents over a few years. The tube makers may have heard of this and decided to re-study their techniques. Miniature was hard to improve (reduced cost had been part of the project) but Octals begged for re-thinking with now-mature technology.
OTOH, we all hated coin-base (perhaps irrationally) and tube makers learned that their few remaining markets would pay the prices for a "real" (old style) base. So coin-base may be a good idea that we rejected.
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PRR - very informative and interesting post. Thank you.
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... Willabe I found a pic of a pair of them. ...
... The only coin base tubes I've ever had were 7591s...
I think mresistor's picture is of coin-base 7591's. The plates look like 7591's, while the plate in the original post is definitely a 6V6.
I've got 2 or 3 coin-base 6V6's hanging around. Most I've seen seem to be G.E. or maybe Sylvania, though I agree with Eleventeen they seem to have been from late-60's to 70's (and maybe a little later).
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OK how about these ... they are marked 6V6 on the top
(http://i782.photobucket.com/albums/yy106/hulakatt/3db38bab-286f-48a8-8ea4-da92eea4b884_zps8666a09e.jpg)
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HBP made the good observation that 6V6 plates are generally solid with no holes (sort of like a 55 gal drum) and no fins where two halves are crimped together. 7591's have holes in the plates and those side fins.
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OK how about these ... they are marked 6V6 on the top
Got a picture of the markings on the top?
I'm confident they are U.S. 6V6's, but look like late blackplates. By that I mean 50's-style blackplate tubes had a coarse surface, and later some manufacturers had smooth/glossy blackplate tubes while most tubes made were grayplate. The Sylvania logos look like 70's-80's era, but the tube designation marking would help pin down whether Sylvania (or some other maker) actually produced that set of tubes.
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(http://i782.photobucket.com/albums/yy106/hulakatt/44978BEC-1148-4E6D-96B6-C438C9442F55-2816-00000203F35116A6_zps18dd6ea8.jpg)
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Yep, that's a Sylvania marking all the way. So the yellow label is accurate; it's a late coin-base blackplate Sylvania 6V6GTA.
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GE made some that way as well. i have a quad of RCA that looks like 80's packing and branding, but they have GE type makings.
they look like these, except for the brand markings: click me! (http://www.ebay.com/itm/Matched-Pair-GE-Coin-Base-6V6GTA-Guitar-Amp-Vacuum-Tubes-Tested-Very-Strong/401003110517?_trksid=p2047675.c100011.m1850&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D33202%26meid%3D42c6930e50f04aca8c00d31499670df9%26pid%3D100011%26rk%3D1%26rkt%3D1%26sd%3D321670925064)
--pete
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A couple of years ago, I bought a 6SJ7 from a tube place ( that I don't remember (CRS) and it was the weird glass type like those pics. It didn't last very long for some reason....noisy....