Tube Rolling w/Crack

[tdogzthmn]

So I found a few tubes in an old radio I was pulling apart today.  The tube all look to be in good condition, no corrosion or cracks.  I dont think I have a way to test them but I though I would list what they are and someone might know if they are worth hanging on to.

1 - 12BA6 unbranded
1 - Sylvania 12AV6
1 - Sylvania 12BE6
1 - RCA 35C5

 

[JC]

If you Google the designations, chances are very good that you will find the data for these types, including what service they were manufactured for.  Remember that in the US designation system, that first number indicates the heater Voltage, so the 35C5 will require a 35 Volt heater supply to operate.

If you happen to live somewhere near a guitar shop that services vintage amps, chances are good that they will be able to test your tubes for you.  If there are any that you can't find on the web, post back; I have a few tube manual reprints that will have them.

[Paul Birkeland]

So I found a few tubes in an old radio I was pulling apart today.  The tube all look to be in good condition, no corrosion or cracks.  I dont think I have a way to test them but I though I would list what they are and someone might know if they are worth hanging on to.

1 - 12BA6 unbranded
1 - Sylvania 12AV6
1 - Sylvania 12BE6
1 - RCA 35C5

 

I'm guessing it was missing a tube?  You can always go to a tube vendor and see what the prices are on these.  I wouldn't necessarily throw them away, but there isn't anything super useful in there.

[Dyna Saur]

The normal tube lineup for this kind of "All American Five"  AC/DC radio is 12BE6 (pentagrid converter)  12BA6  (IF amplifier) 12AT6 or 12AV6 (Detector, AVC and first audio)  50C5 (output stage) and 35W4 (rectifier).  
The filament voltages add up to approximately 121 VAC.  So you are missing the rectifier tube, and may have a wrong output tube, unless there is a dropping resistor in the series-conencted  filament string.

The only tube that has useful audio uses would be the 12AV6, it is essentially half of a 12AX7 and two detector  diodes.  FWIW, 12AT7 is equivalent to half  of a 5751 (plus the two diodes).  These also come in 6.3V filament versions, 6AV6 and 6AT6. Generally  at dirt-cheap "plinker" prices.

/ed B in NC

[Canuck57]

Rolling which tubes (input or power) have the most impact on the sound signature? Or do both equally impact the sound signature?

[Paul Birkeland]

The general rule of thumb (IMO) is that the more gain, the more influence.

Since the 6080 is wired for unity gain, the 12AU7 should have a vastly greater influence on the sound, though there are some special 6080 variants that may suggest otherwise.

[Canuck57]

Thanks Paul...I've ordered a few tubes for my Crack and haven't even rec'd it yet!

12AU7 - NOS Tung Sol, JJ Electronic ECC802-S gold pins and CIFTE (made in France)
7236 Sylvania
6AS7G British Tube CV2523
6AS7G Tung Sol
6as7G RCA

[Dyna Saur]

Speedball arrived on Wednesday June 23rd, I stuffed and soldered the boards, and then did the "demolition" and SB installation Thursday AM June 24th.    Of course, I can never leave anything strictly "stock" so I ended up using 47K, 2W resistors in place of the series connected 22.1 K resistors (they will serve in a future  linestage build).  I also mounted the small red LEDs with the dome side facing away from the boards, as I like to see all ten of  them cheerily glowing when I take a look under the chassis ;-)   The  3K WW resistors still have sufficient remaining lead length, so they will also have a future life in some other project (never waste anything).  

One other minor "twist", due to the way that  I mounted the 100 uF output caps, was to flip them down  into the space vacated by the 3K WW resistors, and under the 6080 cathode SB PCB. There is still plenty of airflow, and the caps don't get too much extra heat. Also gives it a nice "clean" look under the chassis plate.

I also noticed the MJE350s didn't have a metal side, so I did a couple quick B to E and B to C "diode checks", in order to verify their proper lead  positioning.    Everything came up running with no problems,
Those ten little red LEDs  all light up nicely.

With the previously mentioned 6CG7 driver, I get 81V on the VA plates and 6080 grids, and 106V on the 6080 cathodes.  

I'm loath to use audio adjectives, but indeed, the sound is nicer! I'll leave the "flowery"  terminology  to those with more poetic license than I posess.  I'll just say, it sounds excellent with the Senn HD600s.

/ed B in NC

[tdogzthmn]

I found a 12BE6 in an old radio.  Would this tube work in my amp with the speedball upgrade?

[JC]

The 12BE6 is a single heptode.  Not really suitable for audio service; at least I can't think of any audio application for it.

[Dyna Saur]

12BE6 is a pentagrid converter, a seven pin miniature.   Has absolutely no possible use with a Crack, equipped with Speedball or not...    It won't even fit into the tube socket.

What a pentagrid converter does  in a tubed AM radio is to take the incoming signal, mix it against the radio's local oscillator which is tuned to operate 455 KHz above the received frequency, and that then gets amplified in the (you guessed it) 455 KHz Intermediate  (12BA6) amplifier, then on to the detector and first audio amplitier (12AV6 or 12AT6) then to to the single ended pentode power amplifier (generally 50B5 or 50C5). The fifth tube would be a 35W4 half wave rectifier.

/ed B

[Paul Joppa]

To add a bit, a pentagrid (five grids! A triode has only one...) converter is a single tube with a single plate, but which is an oscillator as well as a mixer. This was a very clever bit of high technology, some 70 years ago ...

[tdogzthmn]

Thank you so much for the info!  I think all that stuff is fascinating to learn about.

[tdogzthmn]

I read somewhere that a Tung-sol 5687 would work.  Has anyone heard this tube?

[Paul Birkeland]

I read somewhere that a Tung-sol 5687 would work.  Has anyone heard this tube?

The 5687 could be used with the Speedball, but it would require more than just changing R1 on the C4S boards.  The LED's would need to be removed, then replaced with resistors and bypass capacitors.  5ma and 3v under the cathode should give ~70v on the plates, so that means a cathode resistor of 600 ohms, which should be bypassed by something around 150uf (you could get away with the stock coupling caps).  R1 on the C4S boards should be set for 5ma, I don't have the value sitting her at the moment, but I'm sure PJ can chime in or someone with a C4S manual handy (or the formula handy).

The pinout of the 5687 is also different.

-PB