Grainger49
New member
Dyna Saur said:
Knockout, see this link:
Project Tools
See the first post under More Advanced Tools, and the second post for a link to Harbor Freight where you can buy a set cheap! I have used my set often.
Tube Rolling w/Crack
- Thread starter Dr. Toobz
- Start date
Knockout, see this link:
Project Tools
See the first post under More Advanced Tools, and the second post for a link to Harbor Freight where you can buy a set cheap! I have used my set often.
Natural Sound
New member
Hmmm... now you got me thinking. I still haven't started building my kit yet. Maybe I'll punch the hole out and call up BH for some hole shrinkers. That way I can build the amp stock, get familiar with the way it sounds and then maybe drop in an octal socket and try the 6SN7 later. Are there any other component changes if I go this route?
Go with the octal socket right off the bat and buy some 6SN7 to 12AU7 adapters online. Getting in there to enlarge the hole later will be pretty hard. When you enlarge the 9 pin hole, be sure the socket mounting hole closest to the cooling vents is still a socket mounting hole (so position your punch appropriately), otherwise the speedball upgrade will give you problems.
Natural Sound
New member
Caucasian Blackplate said:
Thanks! Are there any other component changes when going from the 12AU7 to the 6SN7?
Nope, no component changes, just the pinout/socket change.
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
1 - 12BA6 unbranded
1 - Sylvania 12AV6
1 - Sylvania 12BE6
1 - RCA 35C5
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.
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.
tdogzthmn said:
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
New member
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
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
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.
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.
Dyna Saur
New member
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
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
Dyna Saur
New member
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
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
Moderator
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 said:
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
