Tube tester: Sencore MU-150
- Thread starter Brice
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- mu-150 sencore tube tester
dogwan
Dogwan
Here are the rules...
https://audiokarma.org/forumrules.html
Looks like you ran afoul of a strict moderator. I would guess that asking to buy one of the boards falls under the definition of "solicitation"? Feels like a "letter of the law" vs. "intent of the law" situation. You might be a little bit under the microscope being such a new member. I know the moderators have had issues in the past with unscrupulous vendors and hackers trying to fly in as new members and either generate business or take advantage of members.
My suggestion is to send @Brice a private message since he is the creator of the replacement boards. If he doesn't have any extras, at least he can hook you up with the files to have some made and he can tell you who made his initial runs.
PS, notice how I put an ampersand in front of his username. That will flag any user you name and send them a notification that they have been mentioned. It's a sure way to get someone specific's attention, especially us longer time members who turn off notifications for threads to get some peace throughout the day, or at least keep our inboxes somewhat uncluttered.
Good luck.
| Finished up my MU-150 upgrade this evening. Followed Brice's calibration instructions in this thread. All worked as published. I tested a pile of old receiving tubes I had. All tested fine but two. Those two showed shorts. In the trash can they went. It seems to be showing a little more sensitive than prior to board replacement. What was showing 80% is now showing full scale deflection. I re-checked the calibration, fine. Prior to board replacement, my Gm test was not working at all. Now, all tubes except those I trashed showed good Gm. I had to replace my two pushbutton switches. I used DigiKey parts numbers 2368-54-342-ND and 2368-54-347-ND. These are momentary toggles and work just fine. I did have to make an adapter plate to fit inside the existing cabinet. Thank you Brice for a nice board and project. Alton |
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dogwan
Dogwan
@AltonD 's post reminded me that I've been experiencing the same thing. Tubes that used to measure (on emissions) in the "good" range but below 100% all seem to now show at 100% or above. But then some tubes definitely measure as marginal or poor. I've double and triple checked the calibration.
My Gm test is still not working. I've come to the conclusion that my tester may have a faulty "B Load" switch on the Gm settings?
My Gm test is still not working. I've come to the conclusion that my tester may have a faulty "B Load" switch on the Gm settings?
@dogwan, it might have been you who wrote about setting R35. I did that, reran the calibration, and things got better. I was pegging the meter with this one tube. It is now showing a full scale deflection, but not past the scale.
the Gm was not working on the old board and now it does. I tested the transistors on the old board and one was bad. Maybe that was my issue to start with. Might want to check the transistor on the new board. Before I powered the new board up, I rechecked, researched, the pinouts for the three. I had the emitter and collector reversed on all three. Got that fixed and initial power up went well.
the Gm was not working on the old board and now it does. I tested the transistors on the old board and one was bad. Maybe that was my issue to start with. Might want to check the transistor on the new board. Before I powered the new board up, I rechecked, researched, the pinouts for the three. I had the emitter and collector reversed on all three. Got that fixed and initial power up went well.
Done. I had to change R35A to 100 ohm. I could only get 485 Ohms total with R35A @ 10 ohms.
6EA8 1/2 @470 @485 Ohms @510 Ohms
E-122 E-112 E-108
Gm-108 Gm-103 Gm-103
6EA8 2/2 E-120 E-110 E-105
Gm-95 Gm-95 Gm-98
I think the variations in the Gm are due to repeatability with the wire-wound pot. My new switch is not due till first week in December.
6EA8 1/2 @470 @485 Ohms @510 Ohms
E-122 E-112 E-108
Gm-108 Gm-103 Gm-103
6EA8 2/2 E-120 E-110 E-105
Gm-95 Gm-95 Gm-98
I think the variations in the Gm are due to repeatability with the wire-wound pot. My new switch is not due till first week in December.
dogwan
Dogwan
I think I remember doing that, but will have to go back and double check.
Re: the wirewound pot, I did change it out for a discrete resistor pot with 24 steps that I built.
I also have replaced the momentary switch with a much more robust latching switch that Bryce sent me.
The behavior in Gm test mode is there is no meter deflection at all in any Gm settings. However, when the Gm test button is depressed the meter will slightly jump momentarily. I thought it was a bad momentary switch, but am getting the same reaction with the new switch too. So, I am guessing that the meter jumping is just an artifact of changing the electrical conditions in between contact positions of the test button?
bhutchin
New Member
Are you looking at just having the board built, installed, and the unit calibrated, or are you looking at a total rebuild/rewire?
bhutchin
New Member
I bought a Sencore MU150 off eBay a couple of years ago. It was apparently used in a Radio Shack, and the manager charged 50 cents per tube to test. Since the ground connector was cut off the plug, I put the tester in my attic as I did not have an immediate use for it. Well today I opened it up and found some component burn evidence in the center of the circuit board. So it looks like I am going to have to go the route of replacing the board as described in this thread.
One issue I have already is my circuit board does not have the right angle tube sockets. It appears to have a single plate for both the 12AU7 and the OB2 tube sockets. I am hoping I can modify the plate to match the board Brice has so generously made available to us.
Also, there is a small 120 volt power outlet where the power cord comes into the unit. I may get rid of this altogether, and perhaps replace it with a fuse holder. Any suggestions for the fuse rating? I have a Hickok RD-1700, and as massive as that unit is, the fuse is only 3 amps.
I appreciate any suggestions you guys may have. Thank you!
One issue I have already is my circuit board does not have the right angle tube sockets. It appears to have a single plate for both the 12AU7 and the OB2 tube sockets. I am hoping I can modify the plate to match the board Brice has so generously made available to us.
Also, there is a small 120 volt power outlet where the power cord comes into the unit. I may get rid of this altogether, and perhaps replace it with a fuse holder. Any suggestions for the fuse rating? I have a Hickok RD-1700, and as massive as that unit is, the fuse is only 3 amps.
I appreciate any suggestions you guys may have. Thank you!
Hi BassoJay,
I installed a 1A slowblo fuse inside the unit, and kept the power socket, and so far so good: never blew one.
For the socket, I made used an aluminum sheet and cut a plate, made the socket hole, and mount it to the board with 90 degree angle bracket.
I used a Belton socket with shield so the tube is snug nicely once mounted.
I replaced the OB2 with zener diodes so only one socket is now needed versus the original one.
I hope it helps,
Brice.
I installed a 1A slowblo fuse inside the unit, and kept the power socket, and so far so good: never blew one.
For the socket, I made used an aluminum sheet and cut a plate, made the socket hole, and mount it to the board with 90 degree angle bracket.
I used a Belton socket with shield so the tube is snug nicely once mounted.
I replaced the OB2 with zener diodes so only one socket is now needed versus the original one.
I hope it helps,
Brice.
Here is my almost completed MU150 main board. I am waiting for a side mounted tube socket that is currently in USPS Neverland. But I expect it will be delivered over the next week. Thank you, Brice, for making this replacement circuit board available to us! And thank all of you who helped contribute to this project!
