Akai Reel To Reel Capacitors

[Maxxarcade]

I am working on an Akai GX-260D reel to reel that I need some caps for.

The service manual calls the caps "MP capacitors". They appear to be bipolar electrolytics from 250-350v ac.

The problem is, a couple of them are large multi-section caps that I can't find anywhere. The one I need most is 1uf/3uf 350vac, with radial leads.

Can I replace these caps with mylar or poly ones?

Also looking for the cover that goes over the heads.

[Logistics]

Re: Akai Reel To Reel Capacitors

I actually started looking through the Digi-Key catalog, but then thought, "Multi-section bipolar?!?!?!" >_< Don't think I've seen that before.

[PeteS in CA]

Re: Akai Reel To Reel Capacitors

Multi-section lytics? Have those been made since the 50s or 60s? I think looking into individual polypropylene film caps might be a promising route. Just be careful to select AC-rated types or a sufficiently high DC voltage (assuming these aren't safety caps).

[davmax]

Re: Akai Reel To Reel Capacitors

Example cap. http://www.altronics.com.au/index.as...=item&id=R6900

[tvtech]

Re: Akai Reel To Reel Capacitors

I encontered these multisection ac rated lytics in a early 50's 12" stromberg-carlson tv,that had the am/fm radio built in.What a monster that set was,the chassis weighed at least 50lbs alone The power transformer was giant,because the set had two 5u4's in the power supply.Not to mention the hv section had two 1b3's.That was honestly the most complex tube set I ever restored.Now as for your capacitor problem you should be able to replace those with film capacitors of the appropriate value/voltage.You should be able to find those film capacitors at anitque electronic supply, www.tubesandmore.com

[PeteS in CA]

Re: Akai Reel To Reel Capacitors

The power transformer was giant,because the set had two 5u4's in the power supply.

IIRC, the tubes in early tube TVs had have their filaments in parallel, which added to the mass of that transformer.

[Maxxarcade]

Re: Akai Reel To Reel Capacitors

I found what I needed at Digikey. I'm going to use Metalized Poly caps.

See a quick video here:
http://www.youtube.com/watch?v=gNVOpESi9uQ

[Maxxarcade]

Re: Akai Reel To Reel Capacitors

Some progress... Notice the leaking cap on the end

Before:


After:


Now I just need to find some low DC leakage 10uf 50v caps for the audio circuits. They are UCC LL series now, but I don't know if Panasonic FC is good enough. The UCC LLA's are the only low leakage ones I can find, but they are hard to get. Digikey doesn't have them even.

[tvtech]

Re: Akai Reel To Reel Capacitors

IIRC, the tubes in early tube TVs had have their filaments in parallel, which added to the mass of that transformer.

Yep although cheaper sets had them in series string and a single or double selenium diode line doubler power supply,therefore eliminating the power transformer.

[PeteS in CA]

Re: Akai Reel To Reel Capacitors

Those selenium rectifiers looked really interesting.

[Maxxarcade]

Re: Akai Reel To Reel Capacitors

What selenium rectifiers?

[kc8adu]

Re: Akai Reel To Reel Capacitors

selenium rectifiers also smell wonderful when they fail.which they often do.
btw tried to kill the dupes but should have moved them instead of deleting.

[PeteS in CA]

Re: Akai Reel To Reel Capacitors

We got onto talking about early TVs, Maxx. Selenium is a semiconductor that was tried in the 50s. The selenium rectifiers used in TV sets were basically several series-connected diodes (to get the needed reverse voltage rating) in an assembly. Each diode looked like a flat, square, plate, and there were small spacers between each plate that made the electrical connections. I think the intent in that construction was to have decent cooling. The hope was for rectifiers that could handle the power of a 5U4G (later, GB) that would last longer than a tube. The things were a bit leaky, and I'm not sure they delivered the improved reliability. IIRC, selenium was (in the US) declared a strategic material for the military, and set mfrs reverted to 5U4GBs or switched to silicon diodes, which were becoming available. I remember seeing ads for silicon replacement rectifiers that were packaged to fit in tube sockets and also in a form-factor for replacing selenium stacks. TV service people (I learned most or all of this from old magazines for TV service people) were cautioned to be aware that the B+ voltage would be higher, as the silicon rectifiers had a lower forward voltage drop.

Those were interesting days ... vacuum tubes (octal and "miniature"), multi-section lytics (finding exact replacements was not easy, even then, and lytic reliability sucked), point-to-point wiring with chassis mounted tube sockets (no printed circuit boards!), 150V-200V unregulated plate voltages, transistors and semiconductor diodes were just coming into use, customers who tried to fix their own sets by tightening loose screws on the chassis of their set (the adjustment screws for the ferrite slugs in tuned circuit transformers and inductors!), service people always troubleshot to the component level (they had to) and it was cheaper to do repairs than to toss-and-replace.

[PeteS in CA]

Re: Akai Reel To Reel Capacitors

I remember two of the mfrs of selenium and silicon rectifiers ... Sarkes-Tarzian and International Rectifier. In the 70s and 80s, IR created the first commercially viable power MOSFETs and got out of rectifiers in the 80s.

[Maxxarcade]

Re: Akai Reel To Reel Capacitors

I'm quite familiar with tube electronics, I've rebuilt a couple tube sets. I just didn't catch the part where you started talking about selenium until I read further up. I thought you were saying there were selenium rectifiers in the pics I posted. It's almost noon and I haven't been to bed yet, so I'm a little out of it

The first radio I rebuilt and had it work well, was my Grandma's Philco model 46-420. It is one of the transformerless sets, with the 50B5 output tube, and all filaments in series. I think it had a tube rectifier though.

Right now I'm getting ready to rebuild a Sony TC-200 reel to reel, that has a tube/transistor hybrid amp, oil caps, all kinds of fun stuff. I'm a bit concerned about the rubber drive wheels though. They are in bad shape and I doubt it would be worth the cost of replacing them.

We got onto talking about early TVs, Maxx. Selenium is a semiconductor that was tried in the 50s. The selenium rectifiers used in TV sets were basically several series-connected diodes (to get the needed reverse voltage rating) in an assembly. Each diode looked like a flat, square, plate, and there were small spacers between each plate that made the electrical connections. I think the intent in that construction was to have decent cooling. The hope was for rectifiers that could handle the power of a 5U4G (later, GB) that would last longer than a tube. The things were a bit leaky, and I'm not sure they delivered the improved reliability. IIRC, selenium was (in the US) declared a strategic material for the military, and set mfrs reverted to 5U4GBs or switched to silicon diodes, which were becoming available. I remember seeing ads for silicon replacement rectifiers that were packaged to fit in tube sockets and also in a form-factor for replacing selenium stacks. TV service people (I learned most or all of this from old magazines for TV service people) were cautioned to be aware that the B+ voltage would be higher, as the silicon rectifiers had a lower forward voltage drop.

Those were interesting days ... vacuum tubes (octal and "miniature"), multi-section lytics (finding exact replacements was not easy, even then, and lytic reliability sucked), point-to-point wiring with chassis mounted tube sockets (no printed circuit boards!), 150V-200V unregulated plate voltages, transistors and semiconductor diodes were just coming into use, customers who tried to fix their own sets by tightening loose screws on the chassis of their set (the adjustment screws for the ferrite slugs in tuned circuit transformers and inductors!), service people always troubleshot to the component level (they had to) and it was cheaper to do repairs than to toss-and-replace.

[starfury1]

Re: Akai Reel To Reel Capacitors

I used to have one kicking around here but seems its gone


anyway goolged some pics for those wondering what a Selenium rectifier is

http://commons.wikimedia.org/wiki/Im..._rectifier.jpg

http://ampex.hughescatalog.com/elect...enium%201.html


This is just an interesting link by its self on old tech

http://www.xcvcorp.com/Electronics%20Museum%20HTML.html

somewhat interesting too

http://www.theodoregray.com/PeriodicTable/Elements/034/

for those who want a trip down memory lane and for those who are wondering what the old hands are waffling about

Cheers

[PedroDaGr8]

Re: Akai Reel To Reel Capacitors

selenium rectifiers also smell wonderful when they fail.which they often do.
btw tried to kill the dupes but should have moved them instead of deleting.

Maybe because SeO2 (likely product of selenium burning) is highly poisonous.

From the MSDS http://www.jtbaker.com/msds/englishhtml/s1130.htm
Health Rating: 3 - Severe (Poison)
Inhalation:
Highly toxic via inhalation. May cause severe breathing problems that may not appear for several hours after exposure. Irritates the upper respiratory tract. May cause headache, fever, chills.


Typically, most poisons smell horrible (evolution) hence most sulfur compounds smell bad H2S and many others are quite toxic.

[starfury1]

Re: Akai Reel To Reel Capacitors

Dont think they cared too much in those days about health or the environment for that matter.

its even been used as part of the plot in a movie, the old selenium rectifier

How much poetic license has been taken I don't know...they were a bit before my time and old tech then so don't really know much about them and chemical construction (although I don't think the scrappings off one would do what they claimed...but I don't know for sure)

http://antiqueradio.org/tvshow.htm

check "toxicity" under this link for Thallium

Applications: used in semiconductor materials for selenium rectifiers,

http://en.wikipedia.org/wiki/Thallium

one word of warning thought.
Seems you cannot just replace them with diodes,
you need to add resistance.
so be advised to check this out if you ever need to replace one I guess

please keep us posted on how you go Maxxarcade

Cheers

[gonzo0815]

Re: Akai Reel To Reel Capacitors

I have had a lead acid battery charger with selenium rectifiers. The Rectifiers also functioned as an over current protection, if battery was empty.
It was an nice an robust unit which does the job.

[PedroDaGr8]

Re: Akai Reel To Reel Capacitors

Dont think they cared too much in those days about health or the environment for that matter.

its even been used as part of the plot in a movie, the old selenium rectifier

How much poetic license has been taken I don't know...they were a bit before my time and old tech then so don't really know much about them and chemical construction (although I don't think the scrappings off one would do what they claimed...but I don't know for sure)

http://antiqueradio.org/tvshow.htm

check "toxicity" under this link for Thallium



http://en.wikipedia.org/wiki/Thallium

one word of warning thought.
Seems you cannot just replace them with diodes,
you need to add resistance.
so be advised to check this out if you ever need to replace one I guess

please keep us posted on how you go Maxxarcade

Cheers

I know how bad thallium smells. We used to make a compound in one of my labs using Thallium (before we came up with a better route) and in the last step the thallium is eliminated from the compound, we just said it shitted the thallium out because it smelled so bad.