Studio B's Ampex ATR #3-

Constant pink-ish noise only on the output of the right channel when tape is playing off the repro head. Dead quiet when tape is stopped or lifted from the heads. The noise frequency shifts lower at lower speeds, and isn't related to anything recorded (it's there with blank, unbiased tape).

Demagnetized the heads, and transport, and both channels are behaving identically quiet.
The fact that the machine had been recently calibrated, so the repro gains were about the same, and that the noise disappeared at stop led me away from the amps being the obvious target of attention. Poor head grounding is another source of this. However, it's unusual to have such a constant sounding noise with that static discharge/poor ground issue, and only on one channel.

Altec M11/150 Coke Bottle-

Two noisy Coke Bottles, sputtering on one, higher white noise on the other.

Cleaned tube sockets, and capsule connections, then replaced the tubes.
It was the tubes...

More EApreq500 construction and PCB revision work.

-Elsewhere-

Dealing with two fake "Lomo 19a19s"
The power supply looks like a found objects sculpture with the following conditions,
Find parts from an old russian television to build a stereo tube microphone supply.
You can only have 4 screws, some epoxy and tar as fasteners / adhesive.

The mics are a mish-mash of parts, tiny transformer, wrong tube, and probably a Chinese capsule. The capsule looks brand new compared to everything else.
The mic cables are an unusable 6 feet long.
The screen is from the hardware store.

The owner want's to keep the mics as they are, since they are so far from real. I'm building two new mono supplies tailored to the circuit (which is simpler than the real one), and two 20' mic cables.

I don't know if anyone is getting real Lomos off of reverb or ebay these days.

Greg wrote: Sat Nov 04, 2023 9:57 pm
Altec M11/150 Coke Bottle-

Two noisy Coke Bottles, sputtering on one, higher white noise on the other.

Cleaned tube sockets, and capsule connections, then replaced the tubes.
It was the tubes...

Can an Altec 525A (lipstick mic PSU) work with a Coke Bottle Mic? I know a custom cable would be necessary, but are any other mods required? Looking at the schematics I can tell the voltages are pretty close as spec'ed, but the grid arrangement at the tubes is a bit different.

thecr4ne wrote: Mon Nov 06, 2023 5:04 pm Can an Altec 525A (lipstick mic PSU) work with a Coke Bottle Mic? I know a custom cable would be necessary, but are any other mods required? Looking at the schematics I can tell the voltages are pretty close as spec'ed, but the grid arrangement at the tubes is a bit different.

Unfortunately not. They're different animals.

Studio B -

2/xx/20
Electrical Custom rack (built out of a Kepex rack) fuse blew.

Phantom power supply regulator failed (after 18 years) replaced it with newer design.


3/2/20
Mic input #10 on live room mic panel buzz with C12 reliably – check everything
XLR to punch block.

Repunched shield on mic pair at the patch bay.


3/3/20
Eventide instant phaser "depth" control has no effect. I think.

Oddly cycling power restored things.


7/21/20
Console (Neotek Series II) channel 26 not sending audio from monitor pot to direct or bus. Tried using external preamp & returning to insert in, still nothing. Ch.27 no problem.

Dead U7 amp 5534 feeds bus + direct out.

N.B.: This is a feature we modified our board to do, as a type of fader swap, with the mixdown button up.


7/22/20
Monitor output from desk distorting in L.side. Patched across patch bay normals, still distorted, patched "spk B" output to amp, worked fine.

Could not reproduce.


7/21/20
ATR left output low frequency rumble in repro, really quiet

Bad 318H amp (A1) replaced – no.
Replaced Q1 @4 hours in, no noise.

Greg wrote: Wed Nov 08, 2023 5:56 pm

thecr4ne wrote: Mon Nov 06, 2023 5:04 pm Can an Altec 525A (lipstick mic PSU) work with a Coke Bottle Mic? I know a custom cable would be necessary, but are any other mods required? Looking at the schematics I can tell the voltages are pretty close as spec'ed, but the grid arrangement at the tubes is a bit different.

Unfortunately not. They're different animals.

Can you elaborate? Where are the compatibility issues and can a 525A be modded to work with a 150? Are the transformers sufficient at least?

thecr4ne wrote: Thu Nov 09, 2023 10:45 am

Greg wrote: Wed Nov 08, 2023 5:56 pm

thecr4ne wrote: Mon Nov 06, 2023 5:04 pm Can an Altec 525A (lipstick mic PSU) work with a Coke Bottle Mic? I know a custom cable would be necessary, but are any other mods required? Looking at the schematics I can tell the voltages are pretty close as spec'ed, but the grid arrangement at the tubes is a bit different.

Unfortunately not. They're different animals.

Can you elaborate? Where are the compatibility issues and can a 525A be modded to work with a 150? Are the transformers sufficient at least?

The two power supplies are providing different things to two totally different tubes. Other than the basic topology of a 'cathode follower', they aren't the same. You might be able to reuse the 525A's power transformer to build a new supply, double the HT voltage then regulate down to get what's required for the 150. I'm not sure of its power ratings, however and at that point, you're basically starting from scratch and should build a new supply with an off the shelf transformer. I don't remember the details about the 4665 output transformer. It's possible that'd work as a rough substitute.

Greg wrote: Mon Nov 13, 2023 2:15 am

thecr4ne wrote: Thu Nov 09, 2023 10:45 am

Greg wrote: Wed Nov 08, 2023 5:56 pm

Unfortunately not. They're different animals.

Can you elaborate? Where are the compatibility issues and can a 525A be modded to work with a 150? Are the transformers sufficient at least?

The two power supplies are providing different things to two totally different tubes. Other than the basic topology of a 'cathode follower', they aren't the same. You might be able to reuse the 525A's power transformer to build a new supply, double the HT voltage then regulate down to get what's required for the 150. I'm not sure of its power ratings, however and at that point, you're basically starting from scratch and should build a new supply with an off the shelf transformer. I don't remember the details about the 4665 output transformer. It's possible that'd work as a rough substitute.

Do you have any advice for rebuilding the 525a psu? I have a pair with the correct lipstick mics.

I just replaced all the selenium with silicon. Still have to pad down the voltages. Not sure if it’s worth modding them more to be more modern

bikefvcker wrote: Mon Nov 13, 2023 7:31 pm

Greg wrote: Mon Nov 13, 2023 2:15 am

thecr4ne wrote: Thu Nov 09, 2023 10:45 am

Can you elaborate? Where are the compatibility issues and can a 525A be modded to work with a 150? Are the transformers sufficient at least?

The two power supplies are providing different things to two totally different tubes. Other than the basic topology of a 'cathode follower', they aren't the same. You might be able to reuse the 525A's power transformer to build a new supply, double the HT voltage then regulate down to get what's required for the 150. I'm not sure of its power ratings, however and at that point, you're basically starting from scratch and should build a new supply with an off the shelf transformer. I don't remember the details about the 4665 output transformer. It's possible that'd work as a rough substitute.

Do you have any advice for rebuilding the 525a psu? I have a pair with the correct lipstick mics.

I just replaced all the selenium with silicon. Still have to pad down the voltages. Not sure if it’s worth modding them more to be more modern

The original design works pretty well. Nothing like a good old RC chain to keep things quiet, as long as you know what's connected to it always.

Cool. I’ll find my voltage drops i think it’s around 150 ohm. I have a third that was modded with extra part by peluso but that one seems to feedback with low end sources

bikefvcker wrote: Mon Nov 13, 2023 7:31 pm

Greg wrote: Mon Nov 13, 2023 2:15 am

thecr4ne wrote: Thu Nov 09, 2023 10:45 am

Can you elaborate? Where are the compatibility issues and can a 525A be modded to work with a 150? Are the transformers sufficient at least?

The two power supplies are providing different things to two totally different tubes. Other than the basic topology of a 'cathode follower', they aren't the same. You might be able to reuse the 525A's power transformer to build a new supply, double the HT voltage then regulate down to get what's required for the 150. I'm not sure of its power ratings, however and at that point, you're basically starting from scratch and should build a new supply with an off the shelf transformer. I don't remember the details about the 4665 output transformer. It's possible that'd work as a rough substitute.

Do you have any advice for rebuilding the 525a psu? I have a pair with the correct lipstick mics.

I just replaced all the selenium with silicon. Still have to pad down the voltages. Not sure if it’s worth modding them more to be more modern

I recapped mine. Made a thread over at GroupDIY
https://groupdiy.com/threads/recapping- ... 25a.70281/