Name the component

[Lectroid]

At a hamfest today I picked up a homebuilt board with an unknown circuit on it for 5$.  It had two tubes, a 12AU7 and a 12AX7, so I bought it for the tubes.  Picture below.  Maybe a preamp of some kind?

Hung off the 12AX7 was a funny component that I don't recognize.  Picture below, circled.  Looks like three hearing aid batteries soldered together by tiny copper strips...?  Best guess is it's connected from a ground point to pin 2. [Correction: pin 8]

Any ideas what it might be?  Could it just be an kludgy way to bias a tube?

Also, are the black Sprague caps with the red stripes what people here call "bumblebees?"

Also--a box of aluminum chassis.  $1 each, eat all you want.

[shooter]

guessing batteries

[sluckey]

Bias battery and not bumblebees.

[RadioComm]

Also, are the black Sprague caps with the red stripes what people here call "bumblebees?"

They are bumblebee capacitors. There's definitely a market for them. Gibson 58 Les Paul have them. Personally I don't believe the hype. I would never pay 45+ USD for them (for LP values, others go cheaper). Some of them are even fake. They do make repros....

https://www.ebay.com/itm/256097324618?hash=item3ba0970e4a:g:BiMAAOSwEy5kejgP&amdata=enc%3AAQAIAAAAwPcJTRZsJkbfS4AIpHAe596e6aaPHt4h64mM3stKEMh4YuZOTWOVyipcniuPpDI%2BvJ%2BhCgwhvanKIrWKRVk%2FYnuEsHLeGUgxhrvzMxLH3uIsEG5lfgqnEuBcgMQb%2BsLOUotip5U6VeTmrSauST7SE3mVR0ilKRJVAopuELa9hdK6TmugvDDEMiUlxygT%2BNHrOngurFgtQueKguDrjr1OZ%2FDnREElsU8Tuob0DMgAu12btS65abKWeY82lttJWatF1A%3D%3D%7Ctkp%3ABk9SR-iwwq6QYg

https://www.ebay.com/itm/385544015728?_trkparms=amclksrc%3DITM%26aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D20201210111314%26meid%3D8e028cefb9934f71b3d9a37da148b00b%26pid%3D101195%26rk%3D1%26rkt%3D12%26sd%3D256097324618%26itm%3D385544015728%26pmt%3D1%26noa%3D0%26pg%3D2047675%26algv%3DSimplAMLv11WebTrimmedV3MskuWithLambda85KnnRecallV1V4V6ItemNrtInQueryAndCassiniVisualRankerAndBertRecall%26brand%3DVishay+Sprague&_trksid=p2047675.c101195.m1851&amdata=cksum%3A3855440157288e028cefb9934f71b3d9a37da148b00b%7Cenc%3AAQAIAAABUA2rugFlOq3qu1cLac%252F%252Fk6Vp0Oa0HaJIqoXKeIiOR%252BTUgsSvHaeyPxKYu6UqHqq7GaGyKVqHQnjeiiXcQpMGw2t3aB%252BssGfjtIWOBj8wExc7oYYP7xGMyQCrHDyDaSaWjB1CueI3A94n0yxXX5dx5gAC0v0%252BesD72OYYYbrkAZErW5K3sWv7jg1zzLCu31LtYURrpdiCKVplDTa85vwYs77zMUYcGYb7Qf%252FFHCXKTp8HzTrBjCLSm8prnZNtDveEMSnyLnByjEJitMltE3cqzEfQ95CJQn%252BE2F6jLYYZ5fFxpX%252F%252FyiN8FKv3DNGDEj%252Bte7Iyi8NUARCJL8%252BNzybgwJIJmqt%252FJH8%252Fie9jgr%252FJ5TCdK0FVM5jFAjb%252BLs9rcyfnrqf6htARNu8bBDAjQkJ%252Bzmcjr6jLSB4kMmXcOzZE3wwzfCOmCt4lq3bhgt%252B9bhKopg%253D%253D%7Campid%3APL_CLK%7Cclp%3A2047675


Great buy on the chassis box 

[sluckey]

They are bumblebee capacitors.

Bumblee caps have color bands to indicate value. These are not bumblebees.

[RadioComm]

They are bumblebee capacitors.

Bumblee caps have color bands to indicate value. These are not bumblebees.

Indeed. You are correct.  Can't imagine paying those prices for real/fake bumblebees. 

[HotBluePlates]

... Looks like three hearing aid batteries soldered together by tiny copper strips...?  ...

Any ideas what it might be?  Could it just be an kludgy way to bias a tube? ...

Bias battery ...

Fixed-bias for a preamp stage, when building a bias supply was too expensive (and required a tube rectifier diode).  Look around at how commonly a bias of "-1v" to "-1.5v" (or multiples of these values) is seen on a data sheet condition.  The first way to power, light & bias tubes was with batteries.

[Lectroid]

 Well, soldering three shiny-plated batteries together is not my idea of fun, but ham guys probably get off on doing it old school.  Either way, for $5 I got two tubes, 7 of those Sprague coupling caps, a beefy 25K pot for my next fixed bias, and some of the ugliest p2p wiring I've ever seen.  Plus a nice thick plate of copper.  A good day.

Thanks to all.

[HotBluePlates]

Well, soldering three shiny-plated batteries together is not my idea of fun, but ham guys probably get off on doing it old school. ...

Cathode-bias introduces local negative feedback, unless the cathode resistor is bypassed with a capacitor.

Battery-bias causes no negative feedback, and doesn't lower the tube's gain.

It looks like 3 hearing aid batteries will set you back a total of $0.75.  Our host will sell you a 1/2w resistor for $0.60, and a Sprague 25µF 25v cap for $3.44 (or you can get the Illinois budget option for $0.98).



$0.75 for the "Ham's Old School method" vs $1.58-$4.04 for "the Obviously Right Way."  Bias batteries might take more than a decade to wear out & need replacement, close to the timeline we hear preached for electrolytic caps.  Which reminds us to look deeper before poo-pooing the strange way of doing things...

[PRR]

Modern hearing aid batteries are "air-Zinc". They ship with a sticker you remove a minute before you put them to work. They don't seem to last past 9 days even idle, I guess the air depletes the Zinc. However they have ~~twice the energy per size of other types because half the chemistry is air.

The classic grid bias (much less load than cathode bias) is a plain carbon-Zinc cell with very tame electrolyte so it doesn't eat its own guts in years.

[Lectroid]

Bias batteries might take more than a decade to wear out & need replacement, close to the timeline we hear preached for electrolytic caps.

The classic grid bias (much less load than cathode bias) is a plain carbon-Zinc cell with very tame electrolyte so it doesn't eat its own guts in years.

When I dismembered the circuit yesterday, the three batteries together were still putting out 0.56V, even covered in dust and oxidation.

Which reminds us to look deeper before poo-pooing the strange way of doing things...

No poo-pooing here.  I thought it was probably battery bias but always want to learn something new where I can. Good to get confirmation from the experts.   

Thanks again.