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Hello,
I have a pair output-transformers coming from a Sherwood S-5000 amplifier. I found out that this amplifier uses a pair of 7189 (E84L) tubes in the output stage.
Because I would like to use these transformers for building a DIY amplifier, I was wondering if perhaps somebody can tell me what the operating points of the 7189 in this amplifier are?
I am most interested in how much current is going through each 7189 tube in the Sherwood S-5000?
BTW, does somebody knows the 'exact' primary impedance of these transformers and at what percentage UL-taps are taken?
Best regards, Tubecase.
Follow Ups:
If i am not mistaken, some Sherwood 5000 had different output tubes. I recall one with 7868 outputs. regards, Dak
Hi DAK,
Yes, you are correct.
But these output transformers come from the one with 7189 tubes. I am sure of that, because I have seen the chassis.
Best regards,
Kees.
Hi, just checking as i know that the Sherwoods had a lot of different output tube combinations. good luck, Dak
OK, thanks!
Best regards,
Tubecase.
which the 7868 and 7591 version does not.
A friend you get for nothing,an enemy has to be bought
Hi Michael,
Yes, that is correct, these OPT's have UL-taps.
Best regards,
Kees.
Yes, the S5000-II used 7868s, which are electrically equivalent to 7591s.
Fisher, Scott, Sherwood, and (perhaps) other manufacturers took full advantage of the fact that small signal circuitry that successfully drives "12" W. power tubes also successfully drives the 7591 family. I'm on record suggesting "monkey see, monkey do". ;> )
Eli D.
Let us see if we can decipher the real answers to your questions; shall we ?
The Sam's Photofact from Folder 9 Set 475 for the original series S-5000 was tested at 117V AC @ 1.05A in; the power trans #B922J3-3 was rated/tested at 720 VCT@100 mA; 60VCT@150 mA; 5V@2A; 6.3VCT@5.2A. Sherwood used a 1.5A Type 3AG Slow-Blow fuse.
Tubes were 5 ECC83/12AX7 + 1 x 7199 + 4 x 7189 + 1 x 5AR4/GZ34.
The 7189 opt tubes were set up/tested at 413V Ep; 410V Escrn; .5V Ek; -20V Eg.
Since the 60V winding was used for the bias and two 12AX7 filaments, the B+ winding's 100 mA B+ tested rating can be interpreted as 20-25 mA at idle for each 7189.
Now, to interpret the percentage of Ultralinear taps, the DCResistance of the opt is a good indicator. Sam's testers measured from Opt CT to each screen 70 Ohms and to each plate 190 Ohms; approx. 380 Ohms DCR overall plate to plate lead. They measured a primary impedance of 7800 Ohms CT with taps at 800 Ohms CT to 4, 8, 16 Ohm secondaries.
Hoping this helps to answer your actual questions, remember that the size of these opt trannies represents a usual wide bandwidth 25-30 Watt, even 40 watt opt tranny. Personally, I would have no objection to using these fine opts up to 100 mA per half primary winding; but preferably at a lower voltage. I also would trust these as fine sounders without using the UL taps; i.e. for PP 245, VT52 or 250 triodes or 6BQ5/EL84 pentodes...
Hi Interstage Tranny,
Thanks for your answers, these are just the ones I was looking for!
I had been looking on the web and found out that a restored Sherwood S-50000 seems to be a really fine sounding integrated tube amplifier. But since I don't have 7189 and 7199 tubes, and because these tubes are hard to find these days, I don't want to build a copy of the original S-5000.
The reason I asked for the parameters of these OPT's is of course that I want to try other output tubes with these transformers.
Your suggestion of using these OPT's without using the UL-taps is interesting too, this is exactly what I was thinking about too. Since I do have EL84; 6V6 and even some 45 tubes.
Best regards,
Tubecase.
The "iron" you have will work well mated to any of the commonly used "12" W. multi-grid power O/P tubes. The advantage of the 7189 is the ability to squeeze out 20 WPC. The only affordable 7189 equivalent available is the Russian 6p14p-ev, AKA EL84M. NOS is (IMO) prohibitively over priced.
Any number of circuits will work with those fine transformers. Of course, you could "copy" the Sherwood 5000's power section, but suitable small signal pentode/triodes are either "unobtainium" or scarce and getting scarcer. If you go that route, the tube I suggest is the 6BL8. Another possibility is modeling and improving the Dyna ST-35. I'll grind my own axe and suggest you build an "El Cheapo" with triode/UL mode switches. You will not need a preamp with E/C, if 2 VRMS sources, like CDPs, are used. You will be breaking a bit of new ground if E/C style circuitry is used with "fixed" or combination bias and EL84Ms. OTOH, approaching the 20 WPC mark that Sherwood established becomes possible.
Eli D.
Hi Eli,
Thanks for your reply.
You are right that these output transformers are suitable for more tubes than the 7189.
That is exactly the reason for my questions about these transformers, because I don't have 7189 tubes and since these are not easy to find.
So it is not my intention to build a Sherwood S-5000 circuit, but something else.
I will look at the 'El Cheapo'.
Best regards,
Tubecase
The only real electrical difference between the 6V6 and the 'AQ5 shown in the schematic is g2 toughness. The screen grid in a 6V6 is tougher than that in an 'AQ5.
You have stated that you have 6V6s. Build with them and reduce the g2 "safety" resistors to 100 Ω. In order to use the low grade O/P "iron" the schematic shows, triode wiring was essential. You have terrific "iron" and can build with UL/triode mode switches. Also, your superior O/P trafos allow the I/P high pass filter to "corner" slightly below 20 Hz.
A full set of power magnetics can be ordered from Allied Electronics. I'll provide stock #s, if you ask.
BTW, the current production "reissue" TungSol 6V6 is excellent. You would be good to go for many years to come.
Eli D.
Hi Eli,
Thanks for the schematic.
Although I can not build everything, I do like to study on schematics because I can learn of it.
Best regards,
Kees.
6P14P-EV (left), Amprex Bugle Boy 7189 (right).
The 7189 can still be found, but they'll cost you.
I have two matched quads of vintage 7189s' for my Sherwood S-5000, as well as a matched quad of 6P14P-EV Russian tubes from Jim McShane of McShane Design.
In all honesty the Russian tubes are just as good if not better, and for around $85 per quad you can't beat 'em.
I see by the number of posts that your new here. Since Mikey is too humble to say it I will - What Mike Samra says is gospel when it comes to vintage tube gear.
Meat; It's the right thing to do. Romans 14:2
Hello Geezerrocket,
Thanks, it's good to know that the 6P14P-EV Russian tubes are really good replacements for the 7189's.
Best regards,
Kees.
How about he starts with this 6BL8 you drew up and we he can tube from there?
A friend you get for nothing,an enemy has to be bought
Hi Michael,
Thanks for this schematic.
Do you perhaps have an idea how much output voltage ('swing') this circuit can do (within reasonable distortion)?
Would it for instance also be suitable to use this circuit for 45-PP?
BTW, on the schematic is written 'draft', but have you already build this in practise?
Best regards,
Tubecase.
"Would it for instance also be suitable to use this circuit for 45-PP?"
That small signal circuitry can produce something in excess of 50 V. peak to peak, as it takes that much to drive "12" W. tubes and 7591s into clipping. Some extra "grunt" is needed, due to the GNFB loop.
A look at the #45 data sheet indicates that as much as 140 V. peak to peak are needed, depending on the specific operating condition set.
My "seat of the pants" assessment is that you could use that sort of circuitry, IF line stage gain is present.
Eli D.
Dude,
Those are my "hen scratches". ;> ) I "robbed" Sherwood and added some tweaks for a fellow with different O/P "iron" and no o'scope. Compare with the original and notice the brute force method of phase compensation.
Since you have Sherwood O/P "iron", you can copy the original "verbatim", but use a 6BL8.
A nice thing about a pentode I/P stage is the absence of worry regarding C Miller related HF rolloff. Don't try that 1 Mohm grid to ground value with a 12AX7 section.
Eli D.
Hi Eli,
I was thinking, when I would use a pair of 45's with these Sherwood output transformers. Then it might be a possibility to lower the amount of Feed-Back or leave it out totally? Because then the sensitivity of the amp would increase.
Best regards,
Kees.
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