Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dude on November 17, 2019, 12:45:13 pm
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I’ve searched but no luck, anyone know what manufacturer made the Hammond marked EL84’s? Tubes just say Hammond in red but are old from the sixties as l got them fro an AO 43 chassis. Gray plates it
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its my understanding they had telefunken or mullard OEM and relabel them. there should be manufacturer clues in the overall construction.
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My first post.
I have a pair of EL84 tubes from an AO-135 reverb chassis.
They say Made in Holland in white stencil on the top.
On the very bottom in between the pins I have the following codes
rX3
X9A
From the Brent Jesse recording site I did some research and I also have some tube data pdfs from Europe. I may have gotten them from the same website.
The first line
rX = tube code for Philips EL84
The second line
X9A
X = Philips Sittard plant
9 = year so 1959
A = month of January
Check out the Brent Jesse page, or tell me your codes on your tube and I might be able to help you out. I have a bunch of old Mullard preamp tubes as well. There manufacturing codes are similar and are normally found on the side of the tube at the bottom. You may need to hold the tube up to the light to see these codes.
Chappy
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Unfortunately all markings are gone, even under magnification; all that can be read is Hammond which is almost completely faded. But looking at other Hammond organ EL84s, they look identical to Amperex tubes, l believe these are made in Holland, they sound on the bright side but pretty nice tone. I’ve had EL84s with Phillips written on tube and those are Holland tubes, look different then these but are the best EL84s l ever heard. Thanks for the info, much appreciated
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all markings are gone
stick it in the freezer, when it's nice n cool hold the pins n "fog" the tube
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If the freezer fog trick doesnt work then research sold listings on The Bay for Hammond EL-84 tubes. There are several listings on there with the bottom base markings on display and info on what country they came from. Some were Amperex from Holland. There was also a Phillips like mine, and another set from Germany.
The base markings or lack thereof should give you an idea.
Glad to hear that I now have a pair of some of the best EL84 tubes that you have ever heard! Time to put them in my 18W clone and give them a spin.
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Ok, got some markings on bottom of tubes, very small numbers and letters, both tubes seems to have the exact same numbers. They are:
rX3
A9F
These tubes look exactly like tubes on eBay that the sellers says are Amperex.
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rX = EL84
A9F
A = Wiener Radio Werke 'WIRAG; Wein
9 = 1959
F = June
I got this info from the Brent Jesse site
http://www.audiotubes.com/mullcode.htm
I found another hit on the internet for an EL84 with the following code. The page wont open but here is the info:
Real Tube Manufacturer, Wiener Radiowerke. Country, Austria. Etched code on Tube, rX4 A2A. Factory Code, A - Philips, Wiener Radiowerke. Year, 1962.
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Thanks for the info, l mentioned that the Philips EL84s were best l heard, a while back I traded some 5V4s and 5Y3s to a guy in Amsterdam for a bunch of old EL84. He send several sets of tubes with Philips written on them, only some of the Phillips sounded great in my 1974 18 watt. Got ten EL84s in the deal all Phillips but not all were killer, they had D getters.
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Sounds like you made out alright on your trade. Perhaps the ones that didn't sound so good were worn out tubes. Or perhaps as a pair they were badly mismatched thereby affecting performance in your push pull output stage.
Chappy
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I usually match tubes (l don’t have the proper equipment), by putting them in a fixed biased amp and matching the mA readings without changing the bias setting in the amp. This will give me the current draw, maybe not the best way but l have a ton of EL84 unmatched. Unfortunately l don’t have an EL84 fixed biased amp. I might have to change one of my cathode biased EL84 amp to fixed. Thanks for that site, very helpful, but the price of the EL84’s is way out of my range.
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I might have to change one of my cathode biased EL84 amp to fixed
it's WAY easier to give each PA it's own bias R (Rk), measure the vdc at cathode, divide by R value, walla tube current, screens n all :icon_biggrin:
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Shooter, forgive my ignorance but could explain that in a little simpler form, what’s PA stand for?
I take it l can do check the mA draw in a cathode biased amp by putting a 1 ohm R between the EL84’s cathode to ground, measure this and?
Ok, l’m off here, you say give each EL84, it’s own cathode R, measure the voltage across each one, then divide that voltage by the value of the R?
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cathode biased EL84 amp to fixed
see image snippet below, cathode biased PP amp PA section, 2 R's (270 ohms)
measure the VDC at the R/cathode junction, divide by 270, answer tube current per tube.
now keep changing tubes till both are ~~~~~~ =, walla match pair (at idle DCV) what happens under dynamic shredding is complicated :icon_biggrin:
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what’s PA stand for?
power amp
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Two, 270 ohms, those are EL34’s, what value for EL84’s for dissipation of about 11watts.
Two shared EL84s use about 125 to 180, so for each tube to have their own cathode resistor, would that be half of say 150 or 75 ohms?
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I attached an ohms law chart
you need to double the R/tube for single R's/tube
(I'm assuming ~35mA/tube)
so with 1 150 ohm @ 70mA (both tubes) = ~~ 10vdc at cathode
now with 2r's/ tube 10vdc @ 35mA (each tube) =~~~ 285ohms
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I see, l have an SE 6L6 Champ 12, mid 80’s. The cathode R is 390 ohm, on the hot side. My vibro champ, 390, Fender 5F2, one 6v6, uses 470/500 ohm cathode R. If each of those amps was PP, cathode would be 250 ohms. So, with separate cathode R’s with EL84’s in PP, the 270 ohm on each cathode is a good starting point, of course separate caps too.
Now all l have to do is figure out how to use that chart. :icon_biggrin: l will do my homework, thanks
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There is a flavor difference between 1 R and 2, not enough to bother me, but some nuanced tone player :dontknow:
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Yes, some say each their own cathode R, tighter or more like fixed bias, others say no difference. To me there is a decent tone difference but not in the 2 vs 1 Resistor but in the size of the cathode cap. The larger the cap up to a point the tighter the bass. I have used up to 1000uf and l hear a tighter bass with an 18 watt Marshall style amp.
Anyway, l’ll match up the EL84s l have, current wise, most old stock. For all l know l may have completely mismatched power tubes in my EL84 Amps. Thanks for the lesson
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Thanks for that site, very helpful, but the price of the EL84’s is way out of my range.
Yeah his prices are crazy. I think he caters mostly to the hifi market. I have learned a lot from his site though. That is where I got all of my info on European tubes. He also has some Youtube videos where he walks you through his tests for noise and microphonics using a test fixture and an oscilloscope. As well, he demonstrates how he matches both preamp and power tubes using a Tektronix curve tracer. I actually borrowed his idea for the noise test fixture and I find it works really well. Of course, you can also test out tubes for noise and microphonics in the first stage of any guitar amp. And matching power tubes with a curve tracer is probably overkill for guitar amps since we want to add a little colour to the sound.
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Matching tubes by current draw, is difference of no more than 5mA considered matched? The reason I ask is the voltage across the cathode R, can be over 4 volts or more difference to give a 5mA difference and then the dissipation is over 2 watts difference. So, one tube is 12 watt, (4mA difference) the other is 14 watts. Seems with cathode biased amps this way of matching needs to be closer than 5mA to be considered matched, more like within 2 mAs...? Opinions..
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if you still have hair, this is the part you start pulling it out :icon_biggrin:
the "voltage" # is basically your tubes bias point in SE
5mA in the real world is matched
now for fun with amps;
need 2 meters that read ~~ = measuring the same point (poor mans calibration:)
monitor each cathode R junction while playing close to the edge, Ideally your meters have a min/max store function.
after about 10 minutes evaluate the "range" each tube swings, let everyone cool down and swap the 2 tubes with each other, repeat/record/evaluate, have fun :BangHead: