Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => AmpTools/Tech Tips => Topic started by: rafe on June 11, 2008, 08:27:10 pm
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It's a lot bigger than I expected it's a Simpson model 266 with all the probes and a manual .....It's about a foot high with a tilted front and a wood cabinet with a storage door in back for ac cord and probes ...it looks to be new ...but it's 50's .....It may need some work ....fuse looks blown and battery is gone, but I was glad to see that (no corrosion) ....any Idea where to get battery? RMBZ 4 1.34 V or an RM4RT.....It's got 7 condensers but only one is electrolytic ....what are it's chances?? how about the paper and mica's ??
tubes...in probe 9006 in box 6SN7GT & 6X5
0 center D.C. Volts looks handy.
Real work of art ,hope it works Rafe [smiley=sun.gif]
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Well, I can't look at things very long before I have to mess with them ....Put a fuse in and hooked a 1.5 v C battery up ....no good does not measure resistance ....it's supposed to without ac being hooked up....I disconnected battery and plugged it in ....red light came on and tubes glowed Nice JAN 6X5GT, 6SN7GT and a 2A12....I hooked it up to test AC (another tube 9006 diode,in probe) ;D......It read 110 on mine so it's gotta be working on that level ....the battery it calls for seems to be made of unobtainium ....any help out there? ...why wouldn't a duracell work?...I really don't need that function but I'd sure like it if I had it Rafe
PS DC checks out good too ....
PPS Ohm meter works too, when battery is positive grounded ...The manual alluded to that, but was a little vague :o
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> It read 110 on mine
Don't stick VTVM probes in the wall. Since your 266 is not grounded, you have 50:50 chance of finding 110V on the outside of the meter cabinet. If it is grounded like my Heathkit, you blow the house fuse. If you wanna test AC, poke a 6V heater transformer winding.
> does not measure resistance ....it's supposed to without ac being hooked up
No, it needs the DC amplifier (6SN7) to meaure Ohms. No low-volt passive meter will read 10Megs accurately and 100Megs roughly, as this one does. In principle you don't "need" the tube to measure low ohms but they don't bother to switch anything except the range resistor R45-R51.
http://www.simpson260.com/downloads/simpson_266_user_manual.pdf
Replace the main filter cap C7. These meters often "work" when the main cap is incredibly ill, but the calibration will change. 150V, anything from 4uFd to 40uFd. Note that neither side of the main cap is grounded! The tube grids sit near ground, the plates sit high of ground, the cathode resistors run below ground.
The other caps are probably OK unless someone has abused it. It will even work without C1 C2 or C3, unless you are in a strong radio field.
Quite odd to have an Amps function. This will work without power.
> 1.34 V
Mercury. VERY stable voltage. Poisons our children. Can't get it any more.
Use a 1.56V standard bunny-battery. You will have to re-trim R56 "OHMS ADJ", now and every few months. Put in Ohms, high range, get a good short across the terminals, adjust "ZERO ADJ" to zero on the scale. Open the terminals, lower Ohms range, you want to get the needle on the Infinite Ohms mark with R56. If you turn R56 to the end and it still reads off-scale, add 5K in series with R56 to offset the 1.56V/1.34V difference.
Do remember this battery. About 2013 it will start to leak and cause rot inside the meter.
-OR-... half-wave rectify the 6.3VAC onto a 1,000uFd cap to make negative 8VDC. Use the TO220 negative adjustable regulator LM337 (http://www.national.com/mpf/LM/LM337.html) to make a solid -1.25V supply. Dump this on the battery hot terminal. R56 will probably cover the change from 1.34V reference to 1.25V. You don't need any adjustment resistor on the LM337; on the sample schematic, make R2 zero (but you do need the 120R and 1uFd). This may want R45 changed to 9.9 ohms: note that all the Ohms resistors are 1.0 ohms except the 10 is shaved to 9.5 because they expected about 0.5 ohms in the mercury cell. The LM337 should be much more stable, add a 0.4 ohm in series with R45. Test: get a 1% 10R resistor and see what it reads.
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I installed a remote battery holder inside the back trap door , so access is very easy ....I tested a few resistors last night and was very happy with the results, as for DC I just tested the battery it's almost 1.6v
from the looks of this it has never been abused physically...I am truly impressed with the construction of this device, superb neat work, This may sound crazy ,but I'm proud to have this one on the bench :D and if the manual is the original, which seems likely....it was re- calibrated in 57 and again re-calibrated & retubed in 63 .....I don't know what if anything since then ....but it looks like it was handled with care.
Thanks Rafe
Now I can pull the canadian amp out again and check the tremolo!
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seems there is an extra(shielded cable) DC probe, it's got a 2000meg resister in it which looks like it inserts in the well and has a wire with and alligator clip...ground I'll guess, and another plug connected to the shield. It's not in the manual....what's it for? [smiley=embarassed.gif] Rafe
Never mind I have paper addendum on it
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I put an 8ufd cap in today . It doesn't have much room to manuever in there, like an amp does, so I gutted the metal can and slid the 8ufd inside it. I had that cap laying around it's an 8/ 450 volt, I'm believing that it shouldn't matter. Busy week, I need to cap my tube stereo next....got the caps with the maggie order. (different thread) and one can will slip in....but the other is being replaced by 2 caps and I'm not sure how I am going to approach it......may fabricate a little dog house....... ;D
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PRR, you're one of those old world knowledge types that are still indispensible, I swear.