Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by gururyan, Feb 10, 2005.
I just pulled these from an old amp of mine (not guitar), any idea what they are?
The 6CA4 might be but hard to tell, the rest with the exception of the tube labeled USE appear to be Holland made.
So far I can tell it's:
Mullard - Amperex - Sonic? - Amperex - Amperex
Sure, it "appears" yo have a 6CA4 rectifier tube, An Amperex Bugle Boy 12AX7, Not sure what the sonio is but it may be a lower gain preamp tube that appears to be vintage USA made but rebranded, and two Amperex EL84's which are Bugle Boys too.
Amperex Bugle Boys are considered by many to be the best Amperex tube made. Most likely made in Holland but sometimes you'll find a Made in Britain Amperex which would likely be a Mullard manufactured tube. I won't try to go into how they rate aganist some of the benchmark vintage tubes such as Mullard because tone is subjective but if those tubes are tested at a high level, they are nice tubes and worth maybe $25-$35 each foe the EL84's, maybe more if they test new.
The Amperex 12AX7, if tested new could fetch you $20 - $35 on eBay too.
The 6CA4 is a cheap tube moneywise as are most rectifier tubes but it looks like a Mullard as depicted by the worn off Mullard label but 9 pin Mullard ube such as that and the EL84's tend to have the sooty deposits from the factory burn in which has no ill effect at all on their perfromance. A guess on the unmaed preamp tube is a GE or Slyvania without pictoral reference with me.
Does there appear er can you read any codes etched in the glass?
I think I can make some out on the bottom right portion of the far right EL84 maybe?
Thank you very, very much. I don't have a need for EL84 tubes so I guess I need to get these tested and then sell them. I will test the 12AX7 tubes though as I could use them.
On the two Amperex EL84's they both have a "rX2 D7H". (this one is visible in the pic, last tube near bottom of glass)
On the Amperex 12AX7 there is a "47D".
On the Sonio is a "6U8 A".
On the Mullard it looks like a "B7K".
You can use Google to do searches such as Amperex EL84 then the date/mfg code to see if any more info shows up.
The Sonio or Sonic is a 6U8A is just that, A USA made 6U8A preamp tube which were typcally used as a miniature type tube that was used as a combined oscillator and mixer tube.
They have been used as an advanced constant-current technique using a 6U8A tube to operate the 5751 triode voltage gain stage in the most linear manner possible. In addition, the output of the 5751 is optimally coupled to the rest of the circuit and this coupling is such that the 5751 sees virtually no capacitance and no loading at all. <~~~~~~~~~~~~ Hi Fi speak
My friend's step dad builds high end custom home stereo amps and is a tube guru. I just left a message for him, I know he will be more than happy to test these and tell me for sure what I have. He will most likely want to buy them off me. In case he offers, anybody else interested in them after seeing the test results?
Well, he called...he can't test them for me. I will have to go have them tested elsewhere. What kind of fee can I expect for this service?
By the way, I popped the Amperex 12AX7 into my dinky Vox Cambridge practice amp to see if I could hear a difference from the Sovtek it came with...
I was surprised the difference it made, I didn't expect much difference being that it was just a preamp/hybrid "toy" amp. Anyway, this Amperex was noticeably clearer and brighter. I put the Sovtek back in until I can get the Amperex tested...yep, definite difference. I wish I had 2 more so I could toss them in my Fender.
gururyan- Just for interest, your Philips EL84s were made in Hamburg, W. Germany in September, 1957. Many of these were branded as Valvos, also Amperex like these, and lots of other rebrands, with the Bugle Boys I suspect they were sold or supplied in equipment in the U.S. Nice EL84 version, IMO. Many Bugle Boys were made in Holland, but not these, no matter what the screening may say.
The 12AX7 was made in Heerlen, Holland Philips plant in April, '57. The "4" is actually a "sideways triangle" or delta, indicating this origin. Possibly you can find "mC" code above the "(delta)7D". I really like the longplate Dutch 12AX7s, which converted to shorter plate structure during the course of '59 and thereafter (which were still excellent too). They tend to have a definite musical character in guitar amps along w/fine overdrive potential, I feel, although like all other 12AX7s different individual specimens sound different.
The rectifier was indeed made at the famous Blackburn Mullard factory, also owned by Philips, this one in Nov '57.
So I presume they're all likely original to one amp, which was possibly built in around early 1958 or maybe a little later.
I love "excavating" tubes like this out of old equipment, then using them!
This is all VERY interesting to me as I have just recently really "cared" more about tube makes, so finding these has only lit a fire that is sure to add to even more GAS as I consider replacing the tubes in my Blues Reverb.
Great post and fun read, Jeff West
Addendum: tube swapping can yield a wide spectrum of change. Sometimes it's subtle, sometimes it's profound. That's what's so cool about tube collecting and swapping. Of course it doesn't have to be a major pursuit because you typically do find "that special combination of amp and tubes" and stay with it, probably dreading the day those tubes die more than anything
I have a decent stash of tubes. I'm not an expert, just an enthusiast. I have fun with tubes all the time
Is the rX2 code similar to the xf code found on EL34's? I confused the small r meaning Canada but realized the D was the manufacture code
Well, it turns out getting tubes tested in Tulsa, OK is near impossible. I am waiting on a return call from my last hope.
Not even at a TV/Radio/Stereo repair shop?
I have called all those AND the numbers they gave me to try. Two of them were actual TUBE AMP repair shops! I may not have enough knowledge to make this claim, but it seems to me any DECENT amp repair shop would be able to test tubes. Is this a correct statement?
Yes, quite fair! Now that vacuum tubes have seen a resurgence in the muscial world, absolutlely.
I bought a simple vintage tube tester off eBay ($75.00) for my own use at home because I didn't want to hunt like you are doing now. It's not a Hickok 539C but it works fine and has been invaluable for me considering my tube stash numbers in the hundreds right now . . .
Well, my last hope just called...gave me a number to call. This is ridiculous. Anyway, I called that guy and all he had was a broken tester he wanted to sell me for $70.
I guess I will have to sell them as is or keep them in a box for another decade or two...or three.
What a frustrating experience. Note to self, take amp elsewhere for any repair work...Tulsa is no good.