5678 submini tubes - why did I buy them?

[dennism]

Just going through my stash of parts and I came across a small package of submini tubes labeled 5678.   (5 leads coming out the end of the tube in a line).  They've been there for a few years and I can't remember why I bought them.  I'm sure I had a project in mind at the time.   Does anyone know some pedal circuits that would use these?

[Kevin Mitchell]

Very likely for one of frequencycentral's projects - he tends to use these.

Murder One Amp
PentaBoost
Delirium Tremolo/Boost

Probably a few others.

[bluebunny]

Rick's designs used the 5672.  It's slightly different to the 5678.  Someone smarter than me will be along shortly to tell you the difference and if they're interchangeable.

[Kevin Mitchell]

Oops.
The bunny strikes again. You're right!

[amz-fx]

They've been there for a few years and I can't remember why I bought them.  I'm sure I had a project in mind at the time. 

Oh boy, don't I know that feeling!!! 

Best regards, Jack

[Radical CJ]

They've been there for a few years and I can't remember why I bought them.  I'm sure I had a project in mind at the time. 

Oh boy, don't I know that feeling!!! 

Best regards, Jack

I've just found a tube of very obsolete OTAs and am wondering the same thing, why did I buy these? (and I only started tinkering with electronics about 2 years ago)

[vigilante397]

Renegadrian did a version of PentaBoost using 5678, and it looks like thomasha (a pioneer of submini builds, love seeing his work) has used 5678 a handful of times.

[Kevin Mitchell]

I've just found a tube of very obsolete OTAs and am wondering the same thing, why did I buy these? (and I only started tinkering with electronics about 2 years ago)

CA3280?
CA3094?

[dennism]

Wow, faster than a speeding bullet!    And I think the Renegadrian Pentaboost is the winner!    I'm not 100% sure if that's what I was originally planning back in the day, but since it's a vero with about 5 parts and it uses the 5678 tube, why wouldn't I build it?

[dennism]

whoops, might have spoken a bit too soon.    How do I determine which is pin 1 and which is pin 5 on these tubes?    I don't see any obvious markings that would tell me that, but I could be missing something.

[vigilante397]

whoops, might have spoken a bit too soon.    How do I determine which is pin 1 and which is pin 5 on these tubes?    I don't see any obvious markings that would tell me that, but I could be missing something.

I've never worked with 5678, but looking at the datasheet it looks like there should be some sort of marking near the bottom of the tube body that marks pin 1. https://frank.pocnet.net/sheets/127/5/5678.pdf

[amptramp]

The 5672 is a power amplifier pentode but in case you get excited about a submini power tube, it is typically used to deliver 65 mW into a 20,000 ohm output transformer.  It has a similar pinout to the 5678 but the A+ and A- pins are reversed.  The end pin away from the dot is F+ on the 5678 and F- on the 5672.

Here is the 5672 data sheet:

https://frank.pocnet.net/sheets/127/5/5672.pdf

bluebunny was looking for someone smarter to show the comparison.  Instead, he got me, but now you have the datasheets to make a comparison.

[dennism]

Ok, on a couple of the tubes in this packet (Tung-Sol USA marked), I see a little blob of paint next to one of the pins.   Being colorblind, I missed it the first time.    Time to get started on a Pentaboost (not sure what to expect out of it, but it's worth a try).

[bluebunny]

Time to get started on a Pentaboost (not sure what to expect out of it, but it's worth a try).

I did a Pentaboost a while back.  Worth a try.