I did some quick measurements of both chassis, and for our purposes they behave identically.
Max. power is ~15W / 8R @ 1KHz
Bandwidth @ 1.5W / 8R is ~22Hz-20Khz
This is pretty much what I'd anticipated, though I'm still a little surprised that the figures came in as well as they did. Further study is important, but based on what's seen here, these are about as good as any other vintage 15-18W audio amp. And the transformers seem to be just fine-o.
Again, this is with essentially +zero+ mods to the circuit. All I've done is to remove the 12BH7 tube and its 14H plate choke. This is not part of the audio path (that I'm using) and should have no effect on the presentation or measurements. All other mods are cosmetic - removal of Molex connectors, etc. I love it when old stuff still works..
FYI - for these measurements, I'm watching the waveform (sine) with a scope, while I monitor the RMS voltage across 8R with a calibrated Fluke 8050A DMM. The Fluke is quite good well above the audio band, but the scope provides a picture of distortion and a sanity check / back-up of voltage values; calculations are made from the Fluke DMM readings. No, the 8R is not non-inductive.. nor is that an issue at 400Hz / 1KHz where I measure.
Max. power is ~15W / 8R @ 1KHz
Bandwidth @ 1.5W / 8R is ~22Hz-20Khz
This is pretty much what I'd anticipated, though I'm still a little surprised that the figures came in as well as they did. Further study is important, but based on what's seen here, these are about as good as any other vintage 15-18W audio amp. And the transformers seem to be just fine-o.
Again, this is with essentially +zero+ mods to the circuit. All I've done is to remove the 12BH7 tube and its 14H plate choke. This is not part of the audio path (that I'm using) and should have no effect on the presentation or measurements. All other mods are cosmetic - removal of Molex connectors, etc. I love it when old stuff still works..
FYI - for these measurements, I'm watching the waveform (sine) with a scope, while I monitor the RMS voltage across 8R with a calibrated Fluke 8050A DMM. The Fluke is quite good well above the audio band, but the scope provides a picture of distortion and a sanity check / back-up of voltage values; calculations are made from the Fluke DMM readings. No, the 8R is not non-inductive.. nor is that an issue at 400Hz / 1KHz where I measure.
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That's exactly what I've meant. A lead compensation network like the depicted one reduces the open loop gain above a certain frequency and serves, often in common with a lag compensation (i.e. a capacitor or a R/C chain in parallel with the NFB resistor) for maintaining stability of the amp.
I don't think so, as e.g. the good old Mullard 5/10 or 5/20 designs, both dedicated to HiFi reproduction, show R/C networks of the same kind in parallel with the plate resistor of the first valve.
Best regards!
@Kay Pirinha
Thanks for explaining this, you're very helpful. Now I get what you mean by lead & lag compensation.
As to whether or not it's there to compensate for the opt xfmr or the 'key click', I'd tend to agree with you - if the same network(s) show up in other, similar designs that are +not+ devoted to amplifying an organ, then it's pretty safe to say it's not about key-click.
But of course, it might +also+ null the organ key-click as a side effect - hell if I know. But you get what I mean.. =)
Thanks for explaining this, you're very helpful. Now I get what you mean by lead & lag compensation.
As to whether or not it's there to compensate for the opt xfmr or the 'key click', I'd tend to agree with you - if the same network(s) show up in other, similar designs that are +not+ devoted to amplifying an organ, then it's pretty safe to say it's not about key-click.
But of course, it might +also+ null the organ key-click as a side effect - hell if I know. But you get what I mean.. =)
Surely 
!
And compliments to the outcomes of your measurements in post #21. I have to admit that never in my life I would have expected such a good frequency range from your units.
Your reports do encourage me to have a try with two identical output transformers, salvaged from Hammond S6 chord organs...
Are you willing to repeat your bandwith examination at an output power of, let's say, 10 watts? This would tell you some more about the real quality of the output transformers.
If you're, as yet said, basically satisfied with the sonic qualities, just remove anything but the last 12AX7, both 6BQ5's, their related circuitries and, of course, the PSU. Then go with a rectangular input signal @ 10kHz, a dummy load and an oscilloscope and play with the lead and lag compensation to get the optimum, i.e. no ringing, symmetric rise and fall. Have fun!
Best regards!
!And compliments to the outcomes of your measurements in post #21. I have to admit that never in my life I would have expected such a good frequency range from your units.
Your reports do encourage me to have a try with two identical output transformers, salvaged from Hammond S6 chord organs...
Are you willing to repeat your bandwith examination at an output power of, let's say, 10 watts? This would tell you some more about the real quality of the output transformers.
If you're, as yet said, basically satisfied with the sonic qualities, just remove anything but the last 12AX7, both 6BQ5's, their related circuitries and, of course, the PSU. Then go with a rectangular input signal @ 10kHz, a dummy load and an oscilloscope and play with the lead and lag
compensation to get the optimum, i.e. no ringing, symmetric rise and fall. Have fun!Best regards!
Surely
And compliments to the outcomes of your measurements in post #21. I have to admit that never in my life I would have expected such a good frequency range from your units.
Your reports do encourage me to have a try with two identical output transformers, salvaged from Hammond S6 chord organs...
Are you willing to repeat your bandwith examination at an output power of, let's say, 10 watts? This would tell you some more about the real quality of the output transformers.
Sure, I'll try to do that tomorrow evening. Hopefully things hold up as well as they did on the first round..
If you're, as yet said, basically satisfied with the sonic qualities, just remove anything but the last 12AX7, both 6BQ5's, their related circuitries and, of course, the PSU. Then go with a rectangular input signal @ 10kHz, a dummy load and an oscilloscope and play with the lead and lag
Sounds interesting, and if the next series of measurements goes well, then I might take a shot at it. Thanks!
I'm not surprised that decent HF performance is present. A look at the OEM schematic shows that, sometimes, cymbal sounds are produced.
A 10 KHz. square wave may be a bit much, when optimizing phase compensation. Try 2 a KHz. square wave and choose the capacitance based on tilt, ringing, overshoot ...
A 10 KHz. square wave may be a bit much, when optimizing phase compensation. Try 2 a KHz. square wave and choose the capacitance based on tilt, ringing, overshoot ...
What year was yours made? Check for date codes on the pwr and opt xfmrs. Mine are like 23rd week of 65 and 26th week of 66 or to that effect. If yours are of the same era, the psu caps might be just fine - as these are.
My 'daily driver' stereo is a 1962 Fisher AM/FM console chassis that's only had the two 100uF @ 350V parts replaced (front-end voltage doubler) along with the bias supply caps, just for safety. Silly thing, it used those now-impossible ELL80 dual beam-power tubes for the opts. Had to make up these adapter brackets that plug into the chassis and accept a pair (per channel) of EF95, which I'm told is a Euro car radio tube. Works great, though.
I reckon those are 16th & 19th week of '63, respectively - somewhere around May of 1963 then? Again, this is just my own assumption, I have no idea if I'm decoding those dates correctly, but it's typical and does seem to make sense. For now, it's what I'm going with.
Yes, that's roughly what I found, 7-8 years ago. And even so, I expect those are +used+ tube prices? I was able to get 4 pcs. of Mullard & Siemens EL95 in very good shape for around $6/ea including shipping. If you're in the USA, there's a fellow by the name of Jim Sauter who buys & sells all kinds of tubes. He's a very good source for oddball stuff like this, as well as the more common hi-fi & hi-end tubes.
I'm surprised to hear of ELL80's in an U.S. made unit, as I thought they were more common, not to say exclusive, in Europe. EL95's are a good replacement, as they are exactly one half of an ELL80. But they aren't considered as too reliable among radio enthusiasts here. After some tweaking (other cathode resistors, replacing the dial lighting bulbs by, e.g., LEDs, due to the higher heater power requirement), a replacement by 6AQ5's is also possible - same pinout as EL95, but usually much cheaper and more reliable. I've successfully done this surgery on my German Nordmende console from 1965, replacing both ELL80's by four EL90's/6AQ5's.
Best regards!
So far as the power bandwidth goes, I didn't get all of the data I wanted. Thought it best to dive-in and start with a set of full-power (read: worst case) measurements. This went well enough until it reached the 20KHz range and the R335 + C314 network (across the opt primary) smoked out. Guess that needs to be looked at, eh? Why the heck is it there in the first place - what is it supposed to compensate?
But I did manage to collect a little bit of data, which should only be considered very preliminary until conditions are back under control (ha!). First, a table, that might be helpful later - but not so much right now:
Power @ 8R = Vrms (Vrms -3dB)
1W = 2.83v (1.98v)
2W = 4.00v (2.8v)
5W = 6.23v (4.36v)
10W = 8.94v (6.26v)
15W = 10.95v (7.67v)
Now, a set of full-power figures for an arbitrary range of frequencies.
20 Hz = error
40 Hz = 15.51 W
100 Hz = 16.53 W
400 Hz = 17.11 W
1000 Hz = 16.53 W
2000 Hz = 15.96 W
4000 Hz = 16.82 W
6000 Hz = 15.96 W
8000 Hz = 13.78 W
10000 Hz = 13.26 W
20000 Hz = 7.61W (snubber network smoked out here, needs to be re-checked less snubber network).
Seems to be pretty dang good to me, so far. And I also need to point out that I am +not+ entering the audio path where I previously believed.. There are some odd discrepancies between the drawing(s) and these chassis. For one thing, the placement of the WH, GY and RED jacks is confusing and questionable. Presently, signal is being fed to the WH (White) jack, which simply is not the same WH jack as shown in the drawing. The input is actually running to the line marked "INPUT" on the extreme left-hand side of the drawing. Weird.
But I did manage to collect a little bit of data, which should only be considered very preliminary until conditions are back under control (ha!). First, a table, that might be helpful later - but not so much right now:
Power @ 8R = Vrms (Vrms -3dB)
1W = 2.83v (1.98v)
2W = 4.00v (2.8v)
5W = 6.23v (4.36v)
10W = 8.94v (6.26v)
15W = 10.95v (7.67v)
Now, a set of full-power figures for an arbitrary range of frequencies.
20 Hz = error
40 Hz = 15.51 W
100 Hz = 16.53 W
400 Hz = 17.11 W
1000 Hz = 16.53 W
2000 Hz = 15.96 W
4000 Hz = 16.82 W
6000 Hz = 15.96 W
8000 Hz = 13.78 W
10000 Hz = 13.26 W
20000 Hz = 7.61W (snubber network smoked out here, needs to be re-checked less snubber network).
Seems to be pretty dang good to me, so far. And I also need to point out that I am +not+ entering the audio path where I previously believed.. There are some odd discrepancies between the drawing(s) and these chassis. For one thing, the placement of the WH, GY and RED jacks is confusing and questionable. Presently, signal is being fed to the WH (White) jack, which simply is not the same WH jack as shown in the drawing. The input is actually running to the line marked "INPUT" on the extreme left-hand side of the drawing. Weird.
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Interesting, I'll have to look into that! 6AQ5 are much more common here in the USA - you say the two types (EL95 / 6AQ5) are direct substitutes? But what do you mean about dial lamps - did the ELL80 have a heater tap for a lamp - I didn't ever notice that..
As for the ELL80 showing up on this side of the Atlantic, it was clearly a very dumb idea from the first get-go. The type was introduced in 1959, and saw use in the USA by 1961-62.. and then it must have been discontinued shortly thereafter, as they are exceedingly uncommon here. Combing through tens of thousands of tubes over time, I have literally never seen a single example of ELL80 outside of a Fisher in my life.
When I was searching for a (financially reasonable) alternative to the ELL80, about all I found were suggestions to re-wire for a pair of EL95. My particular Fisher chassis uses a fixed-bias supply for the opts, if I recall, so cathode resistance isn't an issue.
Below is a new set of figures showing the behavior at high-frequencies with an 8R load. The circuit behaved quite differently in the upper registers once the R335 + C314 network was removed, and you can see this very clearly in the 10KHz and above range. Please realize that these are nothing like high-precision measurements, just basic benchtop testing that gets me through my day-to-day needs.. but that said, it's not total slop, and the trends should be fairly obvious.
Rl = 8R (semi-inductive I'm sure)
1 KHz = 15.96 W
2 KHz = 15.96 W
4 KHz = 15.96 W
8 KHz = 14.85 W
10 KHz = 14.58 W
12 KHz = 14.05 W
14 KHz = 13.78 W
16 KHz = 14.31 W
18 KHz = 14.05 W
20 KHz = 11.76 W
22 KHz = 11.52 W
24 KHz = 11.28 W
26 KHz = 10.58 W
28 KHz = 9.03 W
30 KHz = 8.61 W
So it's really pretty solid up to 18 KHz or so, and then hits the -50% power point at... 30 KHz? Really? I find that somewhat hard to believe, what say you all? Things went a little wonky with the smoke-out and so on, but I still think these are reasonably accurate readings. Again, I watch waveform shape on an old scope (Telequipment D61) and monitor the RMS voltage on a Fluke 8050A, which is pretty dang unimpeachable for the range where it's being used. It's going to give a true RMS value +/- 1% / 10 counts. per the placard.
Rl = 8R (semi-inductive I'm sure)
1 KHz = 15.96 W
2 KHz = 15.96 W
4 KHz = 15.96 W
8 KHz = 14.85 W
10 KHz = 14.58 W
12 KHz = 14.05 W
14 KHz = 13.78 W
16 KHz = 14.31 W
18 KHz = 14.05 W
20 KHz = 11.76 W
22 KHz = 11.52 W
24 KHz = 11.28 W
26 KHz = 10.58 W
28 KHz = 9.03 W
30 KHz = 8.61 W
So it's really pretty solid up to 18 KHz or so, and then hits the -50% power point at... 30 KHz? Really? I find that somewhat hard to believe, what say you all? Things went a little wonky with the smoke-out and so on, but I still think these are reasonably accurate readings. Again, I watch waveform shape on an old scope (Telequipment D61) and monitor the RMS voltage on a Fluke 8050A, which is pretty dang unimpeachable for the range where it's being used. It's going to give a true RMS value +/- 1% / 10 counts. per the placard.
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No, EL90/6AQ5/6005 and EL95 aren't equivalents or direct subsitutes, they just share the same pinout. The 6AQ5 is a 6V6 in another envelope, thus being much beefier than the EL95. They're cheaper here in Europe also. By checking the datasheets, I noticed that the peripheral components, especially the output transformers, in my console would fit for both of these tubes. So I choose the 6AQ5's.
The caveats: Heater current for the two ELL80 originals is about 1.1 A. Four EL95 would require 0,8 A, so no problem. But four EL90's consume 1.8 A, so I had to get rid of both dial bulbs, thus saving 0.6 A, and replaced these by LED arrangements.
Your measurements on those AO-43's remain quite impressive at full power. Congrats!
Best regards!
Thanks, didn't know that!
My assumption was another one: As far as I know, the only manufacturer of the ELL80 tube was C. Lorenz AG, Stuttgart, which later became Standard Elektrik Lorenz and eventually a part of the big ITT group, with it's headquarter somewhere in the U.S. So the trade paths may have been set up.
Btw, C. Lorenz AG also was Germany's first manufacturer of 7-pin miniature tubes of American origin, such as 6AU6, 6BA6, 6AT6, 6BE6, 6AQ5 etc. They marketed them as EF94, EF93, EBC90, EK90 and EL90, respectively. Yes, it is easy to rework an AA5 radio with tubes of purely German origin, by adding a heater transformer!
Best regards!
Yes, it's interesting news to me, too.
Is this something German radio enthusiasts do? I mean, re-work old US AA5 radios (series heater, hot chassis) and add a transformer, for 6V Euro tubes? Not the sort of thing I would expect, but then again.. why not. If I had a DKE38 or whatever, I'd be trying to make that one work - but you don't see many at all in the US, and for good reason.
I'm not even sure how the sets that are here, even got here in the first place? Servicemen brought them home? Enthusiasts and collectors in Germany sold them to us via post?
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Your observations on DKE38's in the U.S. correspond to mine on AA5's here. I've never seen any. I don't know of any enthusiast who reworked an AA5 this way. But it is possible.
Btw, series heated, hot chassis units are also known here. Especially TV sets were built this way up into the 1970ies. P series tubes (PL84/15CW5, PL519/40KG6...) were dedicated for this purpose. Fabrication of AC/DC powered radios ended in the 1950ies, as AC power grids had become common in our country.
Best regards!
Btw, series heated, hot chassis units are also known here. Especially TV sets were built this way up into the 1970ies. P series tubes (PL84/15CW5, PL519/40KG6...) were dedicated for this purpose. Fabrication of AC/DC powered radios ended in the 1950ies, as AC power grids had become common in our country.
Best regards!