NEC 30m-p23
- Thread starter imready
- Start date
From what I found it seems it's a power pentode, equivalent to a 30A5
http://translate.google.com/transla...?q=NEC+30m-p23&hl=en&rlz=1B2DVFC_enUS213US213
http://www.mif.pg.gda.pl/homepages/frank/sheets/133/3/30A5.pdf
I hope this helps
http://translate.google.com/transla...?q=NEC+30m-p23&hl=en&rlz=1B2DVFC_enUS213US213
http://www.mif.pg.gda.pl/homepages/frank/sheets/133/3/30A5.pdf
I hope this helps
linuxslate
Well-Known Member
Old thread -- back from the dead.
I just bought a Sony TC-200 for $19. I scrapped it. (mechanicals were not great -- parts missing -- evidence of attempted previous repair.)
The plan is to make a simple SE PC speaker amp out of it.
It actually has a total of three 30M-P23's. Two of them driving either the tape heads (record) or speakers (playback). The third 30M-P23 drives the erase head through a really funny looking transformer.
Good news -- for just making a simple audio amp, you get a free spare output tube.
Bad news -- They drove the heaters for all three 30M-P23's off a 90 volt tap of the primary of the transformer (e.g. auto transformer or sort of hot chassis -- one side of the heaters is AC mains, depending on which way you plug it in).
Good news -- That is just one of many primary taps. The thing will run off of various voltages between 110V and 220V, including a 125V pri tap for the "modern world".
Good news --- The rest of the amp runs from the secondary. It's not hot-chassis.
This means that to use it without the "extra" 30M-P23 I need to put a resistor there instead. The data sheet linked to above says the heater current of a 30A5 is 0.15A, so to drop 30V@0.15A, I calculate I need a 200 ohm, 5W resistor. Kind of a waste of perfectly good electrons, but that should not be hard to solder up.
One of the 3 main filter caps is actually split open, but they are all 100µF, so finding them at plenty of voltage should not be a problem. Obviously, there is not such thing as original. I'm going to re-build the entire PS on a piece of perfboard.
Then I am going to put the PC board under a bandsaw, and get rid of the transistor pre-amp and the record/play switching stuff. I just have to be careful to retain or rebuild the global feed back, and I should have a basic power amp.
Not sure if I'll keep the tone and volume controls, or jumper them.
Schematic here:
Sony-TC-200-Service-Manual.pdf
I just bought a Sony TC-200 for $19. I scrapped it. (mechanicals were not great -- parts missing -- evidence of attempted previous repair.)
The plan is to make a simple SE PC speaker amp out of it.
It actually has a total of three 30M-P23's. Two of them driving either the tape heads (record) or speakers (playback). The third 30M-P23 drives the erase head through a really funny looking transformer.
Good news -- for just making a simple audio amp, you get a free spare output tube.
Bad news -- They drove the heaters for all three 30M-P23's off a 90 volt tap of the primary of the transformer (e.g. auto transformer or sort of hot chassis -- one side of the heaters is AC mains, depending on which way you plug it in).
Good news -- That is just one of many primary taps. The thing will run off of various voltages between 110V and 220V, including a 125V pri tap for the "modern world".
Good news --- The rest of the amp runs from the secondary. It's not hot-chassis.
This means that to use it without the "extra" 30M-P23 I need to put a resistor there instead. The data sheet linked to above says the heater current of a 30A5 is 0.15A, so to drop 30V@0.15A, I calculate I need a 200 ohm, 5W resistor. Kind of a waste of perfectly good electrons, but that should not be hard to solder up.
One of the 3 main filter caps is actually split open, but they are all 100µF, so finding them at plenty of voltage should not be a problem. Obviously, there is not such thing as original. I'm going to re-build the entire PS on a piece of perfboard.
Then I am going to put the PC board under a bandsaw, and get rid of the transistor pre-amp and the record/play switching stuff. I just have to be careful to retain or rebuild the global feed back, and I should have a basic power amp.
Not sure if I'll keep the tone and volume controls, or jumper them.
Schematic here:
Sony-TC-200-Service-Manual.pdf
Last edited:
linuxslate
Well-Known Member
Sorry to bump a thread that only I have replied to in 11 years, but just in case anyone ever finds this useful:
My tube tester did not have a listing for a 30M-P23 or a 30A5. A 30A5 also crosses to an HL94, which my tube tester did not list either.
In fact my tube tester apparently does not have a 30V filament setting.
A 35C5 has the same base, so I tested the 30M-P23's with the load setting/socket for the 35C5, but with the filament set one setting lower (I think that is around 25 volts.)
At this setting, the 30M-P23's all tested good, with one of them actually going slightly off scale (>100). I'm sure that's not because these 50+ year old tubes are great, it is probably because a 35C5 has slightly less conductance or gain or whatever my tube tester is testing.
The driver tubes in this recorder are 6267. My tube tester did list these, and with the correct settings, it showed both as OK, but weak. The following tubes are equivalent to a 6267:
6BK8, 6CF8, 6F22
EF86
6Ж32П (6Zh32P)
My tube tester did not have a listing for a 30M-P23 or a 30A5. A 30A5 also crosses to an HL94, which my tube tester did not list either.
In fact my tube tester apparently does not have a 30V filament setting.
A 35C5 has the same base, so I tested the 30M-P23's with the load setting/socket for the 35C5, but with the filament set one setting lower (I think that is around 25 volts.)
At this setting, the 30M-P23's all tested good, with one of them actually going slightly off scale (>100). I'm sure that's not because these 50+ year old tubes are great, it is probably because a 35C5 has slightly less conductance or gain or whatever my tube tester is testing.
The driver tubes in this recorder are 6267. My tube tester did list these, and with the correct settings, it showed both as OK, but weak. The following tubes are equivalent to a 6267:
6BK8, 6CF8, 6F22
EF86
6Ж32П (6Zh32P)
linuxslate
Well-Known Member
'Not sure it is OK to hijack this thread for a build project, but it is relevant, and appearently the only application of the tubes mentioned in the OP for over a decade, so unless someone tells me otherwise, I am going to keep it here.
So, as mentioned, I have parted out a Sony CT-200 RtR tape recorder that used 6267 and 30M-P23's.
Here is the only part I am keeping (both channels):
Note that I intend to keep the tiny level meters.
I have already carefully cut the PC board to retain the outlined section.
Here's the power supply:
C1-1 and C1-2 are a can cap with 2 capacitors, each 100uF @ 180V.
C3 is 100uF @150V, and as mentioned is obviously puffed and split open at the base.
I intend to rebuild the power supply on a piece of perfboard using all new components (except the transformer and possibly the diode.)
Note also that in playback mode, R1 and R3 are in parrallel, so I will hardwire it that way.
As mentioned, I will also add a 200 ohm, 5W resistor to take the place of the heater of the tape bias tube (the 3rd 30M-P23 -- V1).
So here is my question:
Three 100uF caps, basically in parallel? Is that much filtering really necessary?
Yes, I can order (5) 100uF, 450V caps for a couple dollars, but I have a handful of 47uF, 450V radial lead capacitors on hand.
Yeah, I could double up every capacitor, but that would require 6 capacitors.
I also don't want to waste the 3 new capacitors and end up with a buzz.
Given that I don't have the bias circuit, no motor, and no pre-amp stage, and the fact that the modern capacitors are probably "better", would I have enough filtering if I use the capacitors I have.
It should make life easier for the diode -- at least on startup.
So, as mentioned, I have parted out a Sony CT-200 RtR tape recorder that used 6267 and 30M-P23's.
Here is the only part I am keeping (both channels):
Note that I intend to keep the tiny level meters.
I have already carefully cut the PC board to retain the outlined section.
Here's the power supply:
C1-1 and C1-2 are a can cap with 2 capacitors, each 100uF @ 180V.
C3 is 100uF @150V, and as mentioned is obviously puffed and split open at the base.
I intend to rebuild the power supply on a piece of perfboard using all new components (except the transformer and possibly the diode.)
Note also that in playback mode, R1 and R3 are in parrallel, so I will hardwire it that way.
As mentioned, I will also add a 200 ohm, 5W resistor to take the place of the heater of the tape bias tube (the 3rd 30M-P23 -- V1).
So here is my question:
Three 100uF caps, basically in parallel? Is that much filtering really necessary?
Yes, I can order (5) 100uF, 450V caps for a couple dollars, but I have a handful of 47uF, 450V radial lead capacitors on hand.
Yeah, I could double up every capacitor, but that would require 6 capacitors.
I also don't want to waste the 3 new capacitors and end up with a buzz.
Given that I don't have the bias circuit, no motor, and no pre-amp stage, and the fact that the modern capacitors are probably "better", would I have enough filtering if I use the capacitors I have.
It should make life easier for the diode -- at least on startup.
doesn't look like the HV is from an autotransformer to me. I see a 130v secondary winding with proper isolation from the power input. If thats the only diode in there, its half-wave rectified, and voltages look like what I'd expect for a half wave setup. That will need a whole lot of capacitor to filter reasonably. I'd be real tempted to make that full wave rectified and then drop it down to the proper voltage level with filtering. You should get a much quieter supply that way. Its not a center tapped HV secondary, so you'd have to use a bridge rectifier. Output voltage would be roughly double what it is now, so that would require a decently large drop resistor but you could get a pretty quiet supply using a simple CRC filter network.
Input side is a multi-tapped primary for any voltage your heart could desire though. I'd set that for 125v and just insulate the rest of the taps.
Input side is a multi-tapped primary for any voltage your heart could desire though. I'd set that for 125v and just insulate the rest of the taps.
linuxslate
Well-Known Member
@gadget73 . Thanks very much for replying, and for the help.
The autotransformer part is *only* for the heaters of the the 30M-P23's. It's a 90V tap off the primary. Yes, the rest is powered off a properly isolated secondary.
Also, I plan to hard-wire it for 125V as you say. I'll also move the power switch and fuse to the hot side (125V tap), and use a polarized plug to make sure that the 0V side of the primary is the neutral. This will prevent the AC hot side from being present on the PC board.
The little voltage select thing they had was actually a really nice setup, but for what I plan, it's un-needed overkill.
I thought of using a bridge rectifier as you mentioned, but that is a whole power supply re-design. This is supposed to be a quick, low-budget conversion, not a whole design/build project.
Based on your suggestion, I'll stick with the half-wave supply, and order a bag of 100uF caps.
The autotransformer part is *only* for the heaters of the the 30M-P23's. It's a 90V tap off the primary. Yes, the rest is powered off a properly isolated secondary.
Also, I plan to hard-wire it for 125V as you say. I'll also move the power switch and fuse to the hot side (125V tap), and use a polarized plug to make sure that the 0V side of the primary is the neutral. This will prevent the AC hot side from being present on the PC board.
The little voltage select thing they had was actually a really nice setup, but for what I plan, it's un-needed overkill.
I thought of using a bridge rectifier as you mentioned, but that is a whole power supply re-design. This is supposed to be a quick, low-budget conversion, not a whole design/build project.
Based on your suggestion, I'll stick with the half-wave supply, and order a bag of 100uF caps.
ah, ok I see what you mean about the heaters.
well, if you're not totally opposed to leaving the heaters as-is, you could run the two output tubes in parallel between the 90v and 120v taps. A proper transformer would be better though.
I'd make it full wave, but largely because I don't much like half wave supplies. Too noisy, and with a single ended amp you need all the help you can get. A nice drop resistor between first and second caps would give a considerably quieter supply with a bunch less capacitors. I'd set the plate volts to whatever the datasheet allows as max too, may as well get all the power it can make.
well, if you're not totally opposed to leaving the heaters as-is, you could run the two output tubes in parallel between the 90v and 120v taps. A proper transformer would be better though.
I'd make it full wave, but largely because I don't much like half wave supplies. Too noisy, and with a single ended amp you need all the help you can get. A nice drop resistor between first and second caps would give a considerably quieter supply with a bunch less capacitors. I'd set the plate volts to whatever the datasheet allows as max too, may as well get all the power it can make.
linuxslate
Well-Known Member
Ooooh... I would have probably never thought of that.
I guess I should get some credit for being wise enough to seek the wisdom of others. I did find a fat ceramic ceramic resistor that measures 230 ohms, and I figured that would also go slightly easier on the heaters of the remaining tubes. But 1st, I am not sure that it's rated at the needed wattage, and 2nd, doing it like @gadget73 says is more energy efficient (easier on the power transformer). Yeah, I'd have 120VAC on the PCB, but I pan to make it finger safe anyway.
---> Full Wave
I had also thought of the fact that like @Tom Bavis mentions -- Using a bridge would also go easier on a old power transformer.
---> Sticking with Half Wave
At the same time, I found (2) new Rubycon 120µF @ 360V capacitors in my bin. I bought them locally, so I should be able to get more.
---> Full Wave
But then I found a 8A, 200V bridge rectifier.
The consensus is clearly bridge, and I'm all for efficiency, and going easy on an old power transformer, so I guess that is what I will go with.
I just downloaded PSU Designer II, and it seems to run fine under Linux/Wine, so I guess I'll play with that.
linuxslate
Well-Known Member
Update on my build project:
What I am doing: I am trying to make a small and basic SE power amp out of the guts of a Sony CT-200 RtR tape recorder. It's intended use is for a basic PC speaker amp.
Build Status: I have built it up on what used to be a polymer cutting board. (It is literally a breadboard project). I succumbed to peer pressure, and took both suggestions: 1)To design/build my own bridge rectifier HV power supply, and 2) to use the 90V and 120V taps to get 30V for the 30M-P23's.
This project has involved far more construction type work than I thought. It's ended up as kind of like an erector set -- with everything bolted together with dozens of 4-40 and 6-32 nuts and bolts. It's built exactly like a commercial product never would be built. Where possible, I have even reused brackets and other hardware from the Sony tape recorder. Even the input RCA jacks are re-used.
I settled on an 8 x 10 inch size for the chassis before the decision to build my own bridge rectifier supply, and I also ended up using some brackets from the original transport mechanism to hold the power transformer. These 2 factors caused me to have almost no room for the rest of the power supply. The power supply is built on 2 small terminal strips that are far more "crammed in" than they should be.
If this thing doesn't buzz, I'll be amazed.
Electrical Status: I have powered it up with the B+ disconnected. I measured about 7V on the 6267 filament pins, and about 27.8 on the 30M-P23 filament pins without the tubes. I figure that is fine. I installed the tubes (B+ still disconnected), and the tubes appeared to glow normally. Note that doing the 30M-P23 filaments this way means that one side of the filaments is the AC hot side. 30M-P23's are rated for an elevated heater of 150V, so this should be fine.
I was getting about 170V no-load on the B+.
I have now connected the B+, but a really stupid wiring error caused a positive smoke test. It was very minor, and I corrected it, but I need to make sure nothing else was damaged before I try again.
I also measured about 35VAC between the transformer mounting bracket and AC ground. There is also about the same voltage from the amp ground to AC ground. Note that I am using a polarized 2 wire AC Cord, so amp ground and AC ground should be isolated. Also, I did this test when I had no load on the Power supply (filaments or B+). There is no "Death Cap" or anything else that would obviously explain this.
Note also that I was measuring from the power transformer outside (laminates and mounting) to the chassis of an unrelated and powered off bench power supply that I believe to be properly chassis grounded. I plan to re-try the measurement with the amp wiring completed (PS under load), and directly to my bench power strip ground.
Is this normal for an ungrounded unit? What would one expect the voltage to be between an (supposedly) isolated transformer and AC mains ground? Is this just because my scope meter has a really high input impedance?
What I am doing: I am trying to make a small and basic SE power amp out of the guts of a Sony CT-200 RtR tape recorder. It's intended use is for a basic PC speaker amp.
Build Status: I have built it up on what used to be a polymer cutting board. (It is literally a breadboard project). I succumbed to peer pressure, and took both suggestions: 1)To design/build my own bridge rectifier HV power supply, and 2) to use the 90V and 120V taps to get 30V for the 30M-P23's.
This project has involved far more construction type work than I thought. It's ended up as kind of like an erector set -- with everything bolted together with dozens of 4-40 and 6-32 nuts and bolts. It's built exactly like a commercial product never would be built. Where possible, I have even reused brackets and other hardware from the Sony tape recorder. Even the input RCA jacks are re-used.
I settled on an 8 x 10 inch size for the chassis before the decision to build my own bridge rectifier supply, and I also ended up using some brackets from the original transport mechanism to hold the power transformer. These 2 factors caused me to have almost no room for the rest of the power supply. The power supply is built on 2 small terminal strips that are far more "crammed in" than they should be.
If this thing doesn't buzz, I'll be amazed.
Electrical Status: I have powered it up with the B+ disconnected. I measured about 7V on the 6267 filament pins, and about 27.8 on the 30M-P23 filament pins without the tubes. I figure that is fine. I installed the tubes (B+ still disconnected), and the tubes appeared to glow normally. Note that doing the 30M-P23 filaments this way means that one side of the filaments is the AC hot side. 30M-P23's are rated for an elevated heater of 150V, so this should be fine.
I was getting about 170V no-load on the B+.
I have now connected the B+, but a really stupid wiring error caused a positive smoke test. It was very minor, and I corrected it, but I need to make sure nothing else was damaged before I try again.
I also measured about 35VAC between the transformer mounting bracket and AC ground. There is also about the same voltage from the amp ground to AC ground. Note that I am using a polarized 2 wire AC Cord, so amp ground and AC ground should be isolated. Also, I did this test when I had no load on the Power supply (filaments or B+). There is no "Death Cap" or anything else that would obviously explain this.
Note also that I was measuring from the power transformer outside (laminates and mounting) to the chassis of an unrelated and powered off bench power supply that I believe to be properly chassis grounded. I plan to re-try the measurement with the amp wiring completed (PS under load), and directly to my bench power strip ground.
Is this normal for an ungrounded unit? What would one expect the voltage to be between an (supposedly) isolated transformer and AC mains ground? Is this just because my scope meter has a really high input impedance?
linuxslate
Well-Known Member
Thanks, @gadget73 -- That is what I think, too, but I intend to check into it a little more.
The power transformer is very old and dry feeling, but I have no reason to suspect a short. All output voltages seem nominal, and it does not smell. It is fused with a 2A fast-blow fuse.
Also, in looking at the schematic, I probably did not damage anything with my wiring error. The resistor that smoked is not used any more the way I am setting this up as just a power amp.
Essentially, I connected the screen voltage to R123 instead of to the tube screen and R4 in the snippet shown a few posts up. (although it was the other channel, so it was actually R223).
So the path was R223 --> VU Meter trim pot --> OPT secondary winding --> ground.
It looks like a diode would have protected the tiny VU meter, and given the amount of upstream resistance, I doubt I hurt the OPT winding. The diode would have to have really low ratings for me to have zenered it (all diodes can work as zener diodes once). I don't know if I damaged the trim pot.
(I have to admit to researching as I type this, so thanks to any readers for bearing with me.)
Point is that it looks fine to power up again now that the mistake is corrected.
Pictures -- and possibly a sound report -- soon.
The power transformer is very old and dry feeling, but I have no reason to suspect a short. All output voltages seem nominal, and it does not smell. It is fused with a 2A fast-blow fuse.
Also, in looking at the schematic, I probably did not damage anything with my wiring error. The resistor that smoked is not used any more the way I am setting this up as just a power amp.
Essentially, I connected the screen voltage to R123 instead of to the tube screen and R4 in the snippet shown a few posts up. (although it was the other channel, so it was actually R223).
So the path was R223 --> VU Meter trim pot --> OPT secondary winding --> ground.
It looks like a diode would have protected the tiny VU meter, and given the amount of upstream resistance, I doubt I hurt the OPT winding. The diode would have to have really low ratings for me to have zenered it (all diodes can work as zener diodes once). I don't know if I damaged the trim pot.
(I have to admit to researching as I type this, so thanks to any readers for bearing with me.)
Point is that it looks fine to power up again now that the mistake is corrected.
Pictures -- and possibly a sound report -- soon.
linuxslate
Well-Known Member
Working and playing music!
For those just tuning in, I am describing a basic PC speaker amplifier that I made from the remains of a Sony CT-200 RtoR tape recorder. It uses the 30M-P23/30A5 tubes that are the topic of this thread.
My daughter picked "Ice Queen" by Within Temptation for the first test with actual music.
Both channels play sound, and seem within balance, although for this first test, my speaker placement was not ideal. For testing it was connected to my Vintage Sony 3", 2 Way bookshelf speakers.
It does have a ear-to-speaker level hum, probably straight 60hz, but it is not noticeable with music playing. It gets worse if I put my hand near the input terminals. It was also sitting right under my bench magnifier light, which is fluorescent.
The power transformer shell and internal return -- to AC ground voltage that I saw previously, is now gone. It was either from having no load, or just a test issue.
Interestingly, one VU (level) meter is not working, but it is the channel that was not associated with the wiring error mentioned previously. Troubleshooting tomorrow.
It has plenty of power for a PC speaker amp. Definitely will go louder than my last project, the sub-mini tube amp, before beginning to distort - at least to my ability to detect.
Initial input was from my mobile phone, and I also connected it to my PC. There was no evidence of a ground loop when connected to the PC.
Right now, my home-designed power Supply is pretty close to the intended voltages, and there is no evidence of anything getting hot. The bridge rectifier seemed to be slightly warm when checked a few minutes after shut-down (having run for at least 1/2 hour.)
Here is a screen shot from PSU Designer of the power supply as currently implemented:
Don't get too hung up on the exact parts/values. They didn't have "That salvaged bridge rectifier at the back of your bench" as one of the choices.
With these values, the plate and screen voltages are a little "conservative." (Read as "Almost 20 volts too low"). Upping the voltage a bit may give me a tiny bit more room before the onset of the distortion, but the smart money is probably on "leave it as is."
A few notes on the pictures below:
-- Please understand that it will be fully or mostly enclosed. These do not show the intended end-state. I will make a Lexan top that will fit the stand-off over the PC board. The higher area of the back will be enclosed in the garbage can metal mesh. I plan to add some copper tubing for a slight "Steam Punk" look.
-- The loose purple wires are 6.3VAC. These will be used to run some LEDs. (But not under the tubes! Ihate that. OK, perhaps "hate" is not appropriate in our politically correct world -- I have a personal preference against LEDs under tubes.) I'm going to try to arrange them to make some sort of cool effect with the Lexan.
-- I'll either mount the VU meters, or replace them with LED meter bars.
-- Note that the AC line cord grommet/strain relief used to be one of the tape motor vibration isolators.
I'll upload more picts when the project progresses.
For those just tuning in, I am describing a basic PC speaker amplifier that I made from the remains of a Sony CT-200 RtoR tape recorder. It uses the 30M-P23/30A5 tubes that are the topic of this thread.
My daughter picked "Ice Queen" by Within Temptation for the first test with actual music.
Both channels play sound, and seem within balance, although for this first test, my speaker placement was not ideal. For testing it was connected to my Vintage Sony 3", 2 Way bookshelf speakers.
It does have a ear-to-speaker level hum, probably straight 60hz, but it is not noticeable with music playing. It gets worse if I put my hand near the input terminals. It was also sitting right under my bench magnifier light, which is fluorescent.
The power transformer shell and internal return -- to AC ground voltage that I saw previously, is now gone. It was either from having no load, or just a test issue.
Interestingly, one VU (level) meter is not working, but it is the channel that was not associated with the wiring error mentioned previously. Troubleshooting tomorrow.
It has plenty of power for a PC speaker amp. Definitely will go louder than my last project, the sub-mini tube amp, before beginning to distort - at least to my ability to detect.
Initial input was from my mobile phone, and I also connected it to my PC. There was no evidence of a ground loop when connected to the PC.
Right now, my home-designed power Supply is pretty close to the intended voltages, and there is no evidence of anything getting hot. The bridge rectifier seemed to be slightly warm when checked a few minutes after shut-down (having run for at least 1/2 hour.)
Here is a screen shot from PSU Designer of the power supply as currently implemented:
Don't get too hung up on the exact parts/values. They didn't have "That salvaged bridge rectifier at the back of your bench" as one of the choices.
With these values, the plate and screen voltages are a little "conservative." (Read as "Almost 20 volts too low"). Upping the voltage a bit may give me a tiny bit more room before the onset of the distortion, but the smart money is probably on "leave it as is."
A few notes on the pictures below:
-- Please understand that it will be fully or mostly enclosed. These do not show the intended end-state. I will make a Lexan top that will fit the stand-off over the PC board. The higher area of the back will be enclosed in the garbage can metal mesh. I plan to add some copper tubing for a slight "Steam Punk" look.
-- The loose purple wires are 6.3VAC. These will be used to run some LEDs. (But not under the tubes! I
-- I'll either mount the VU meters, or replace them with LED meter bars.
-- Note that the AC line cord grommet/strain relief used to be one of the tape motor vibration isolators.
I'll upload more picts when the project progresses.
Attachments
linuxslate
Well-Known Member
Updated picture.
I've been working on this between holiday events, and a cold.
Still working on getting the copper pipes to fit/look right. I already made it better than in this picture. The only thing missing is the mesh that will enclose the area where the transformers are. It actually needs to be a pretty big piece to fold into the need shape. I may need to purchase another metal mesh garbage can.
The copper pipes are not intended for lifting, and once the mesh is installed there will not be so much of a tendency to want to pick it up that way.
I may make a "skirt" for under the plexiglass. There is a place where it would not be too hard for a wayward finger to come in contact with B+ on the right side. I at least need to do something for that side.
I haven't looked at what may be causing the one VU meter not to work.
I've been working on this between holiday events, and a cold.
Still working on getting the copper pipes to fit/look right. I already made it better than in this picture. The only thing missing is the mesh that will enclose the area where the transformers are. It actually needs to be a pretty big piece to fold into the need shape. I may need to purchase another metal mesh garbage can.
The copper pipes are not intended for lifting, and once the mesh is installed there will not be so much of a tendency to want to pick it up that way.
I may make a "skirt" for under the plexiglass. There is a place where it would not be too hard for a wayward finger to come in contact with B+ on the right side. I at least need to do something for that side.
I haven't looked at what may be causing the one VU meter not to work.
is the meter coil open? Doesn't take much to kill those. I've also had them mechanically jam before from tiny amounts of dirt. Often if you very carefully back the pivot screw out a tiny amount it will un-stick and work properly. Done that with loads of CB radio signal meters.
linuxslate
Well-Known Member
Using my DMM on resistance, the working movement pegged, and the broken one did not move at all. The needle was free if you shook the meter.
When the meter did not move, I didn't even notice if there was an out-of-circuit resistance or not.
I gave it a once-over for anything obvious (like a very fine wire leading from the terminals into the meter), and then gave up.
The meters have been cut off and disposed of. The one that was working had a broken mounting ear. I saw no point in keeping them.
Not sure at this point if I'll just leave it as is, or order a stereo LED bar graph module.
I have a 1950's radiation meter that suffers from chronic meter stiction. I'll work with it by getting it to move, and then gently tapping it until it returns to zero, then repeating for a long enough time to surely result in a diagnosis of Asperger's. When it is working relatively well, I put it away for 5-10 years, and the stiction returns.
It's not just one of the common, yellow, CD ones, so I try to keep it working.
When the meter did not move, I didn't even notice if there was an out-of-circuit resistance or not.
I gave it a once-over for anything obvious (like a very fine wire leading from the terminals into the meter), and then gave up.
The meters have been cut off and disposed of. The one that was working had a broken mounting ear. I saw no point in keeping them.
Not sure at this point if I'll just leave it as is, or order a stereo LED bar graph module.
I have a 1950's radiation meter that suffers from chronic meter stiction. I'll work with it by getting it to move, and then gently tapping it until it returns to zero, then repeating for a long enough time to surely result in a diagnosis of Asperger's. When it is working relatively well, I put it away for 5-10 years, and the stiction returns.
It's not just one of the common, yellow, CD ones, so I try to keep it working.
