Anyone know tube amp service, mods, etc?

Johnny Jaded

I have an old tube amp I would like to do some stuff to and have some questions. I'm building a new cab for it as well as an add'l 1x12 speaker cab, but my questions are all about wiring and electronics.

It's an early to mid 60s Airline 55W 1x12 combo with vibrato. I have been unable to find the original schematic. It has two 6V6GT power tubes, two 12AX7 preamp tubes, a 6X4 rectifier tube and a 6AU6 (preamp?) tube for the vibrato. It has a Jensen C12-R speaker which I would like to match for the extension cab.

Some things Id' like to do...
1-Avoid being electrocuted.
2-Change to a 3-prong power cable for proper ground.
3-Properly add a speaker jack to power an additional 12\" speaker cab. I have little knowlegde of impedence, but understand it is important. I haven't a clue how to find what it is on the existing speaker or the amp.
4-Replace all the tubes and \"bias\" the power tubes as necessary.
5-Properly add an effects loop. Parallel or series?
6-Properly add a standby circuit with switch and yellow gem light. This would include moving the existing fuse holder and the foot switch jack to the back to put the new switch and light beside the existing power switch and red gem light.

Thanks for helping a brother out.
Johnny \"Sparks-a-flyin\" Jaded

archon

seeing as JJ started a thread about tubes (valves!) can i tag a stoopid newbie question on the end;

should a tube glow if its working - ie: if the tube in the poweramp of my amp isnt glowing does it mean its dead? or would that mean there'd be no sound?

guitar3456

Tube filaments must glow..if not it's probably bad. If it's a preamp tube, it may contribute to a weaker tone. Depends on where it's used.

Amp Mods- NO 1. Avoid it if you have no electrical experience. you can get knocked around by lethal voltages and currents in tube amps especially. Never solder or make connections when until unit is fully discharged.. ie caps must be bled etc. Safety first

Grounding the amp is easy. Same connection White/Black but add a bolt and nut to the metal chassis frame and connect the green ground wire there.

Standby's- depends on which..some just keep the filaments powered, others keep filaments and bias voltage and remove the plate high voltage dc. For the Amp SB light, that would be in series with the supply line of the bias or 6-12v supply. Some set it up so the light comes on in SB, others prefer it off... yada yada personal preference I guess.

Bias- very tricky without proper equipment. If it's \"too cold\" you'll get nasty distortions. many mgs do not have bias adjustments. They are fixed by the hard wired components. Changing the tubes in this case would suffice..unless the bias components are defective, or out of tolerance.

Loops- parallel are better cause you can mix the amount of amp signal with the efx level. Serial breaks the loop and inserts it from that point. It depends if you want a pre power stage loops, or pre EQ loop. Either are very difficult to install without a reference point or schematic which may be hard to find.

EXT CAB JACK
Impedance- even if your speaker is currently 8 ohm, most Tube amps and components can handle a 4 ohm load (2- parallel 8 ohm cabs). If not, most of the time an amp that is mismatched will motorboat. That is this fluttring noise that sounds like a idling motor even when you don't play a note.
You can add a jack by simply connecting a new 1/4\" jack and wiring it in parallel. Sleeve to ground, tip to signal or \"+\" wire. DO NOT USE SHORTING TYPE JACKS...many have and BOOOM!!!!!!! Again, this will reduce the impedance and effectively double the power (current) in the power amp. You must be sure the main power supply current available is adequate to support higher currents..if not, it'll blow the main power fuse in the amp. Most Power Supplies of that era are beefy enough to handle it, but check to be sure. If you have a 2 or 3 amp fuse...I'd say NO. At that point the only other option is a series extension cab that now would be 16 ohms.

zap

If this typo \"ARLINE\" is in fact \"AIRLINE\", then someone on ebay has a CD with ~~1200 amp schematics.
http://cgi.ebay.com/aw-cgi/eBayISAPI.dll?ViewItem&item=4823127300

Another site lists Airline schematics http://justradios.com/PA.html

and an amp for sale maybe like yours also on ebay for a stereo stack?
See eBay item # 7383831804

...better let my dial-up cool off now...

Johnny Jaded

Zap!?! Thanks for the links.

Mine is 62-9013A. I can see some similarities, but it's different. I'm guessing when it was made. Could be 70s. The cab on mine is particle board & plywood with black tolex. Junk. The head was in the top of the cab with a similar mounting plate with the knob access on the front. But... that's all over now. Now it's getting... something different. Let me just say... glow in the dark chicken head knobs. :shock:

I have found a couple schematics for airlines, but not for mine. The closest I have came is a 100W 2x12. It is most certainly a knock off, I mean it was made for Wards. I imagine it could be electronically identical to a Fender Vibro-something-or-other, but I haven't a clue which one.

How can I tell the impedence of the existing speaker and what the amp can handle? I don't see it printed anywhere.

I'll try to post a pic or two.

Thanks for all the info and advice.

Smoldering' Johnny Jaded

Tal Rules

You might give this a shot Old jaded one...
It's maybe a little closer...
http://tdsl.duncanamps.com/schematics2.php?make=Arline

Pretty good site for amps schematics and tube specs..
Had a problem with my Roland JC50 a while back and fixed it useing their JC schematic..
Was close enough...

Hope this helps..

See Ya,
Tal

zap

\Johnny Jaded\ wrote:

Mine is 62-9013A.

This shows a GDR-9013A. Same? http://www.candisc.com/ranger/manuals3.htm under Wards Airline.