Ampeg Retube Question

[MrB]

Greetings,

 

I'm about to retube my 1966 Ampeg J-12-D Jet, and have a couple of questions for the tube experts in the club.

 

1. Two Power tubes - 7868

Electro-Harmonix has recently started production of a new 7868, a matched pair retails for around $66. NOS tubes are available for about twice that price. I'm leaning toward the NOS, but the cost is a big issue. Has anyone compared the EH to the original? How do they sound? My experience tells me the NOS will last longer.

 

2. Two preamp tubes - 6BK11

These are out of production, NOS are all gone.

Does anyone know which other tubes would work in their place? A blog on the web said 6C10 are close enough, another mentioned 6K11. Both of these are available as NOS for around $40.

Obviously, I'd like some assurance that my amp won't be reduced to a smoldering pile of melted electronics before I stick the alternate tubes in.

By the way, I only plan on replacing V2, the actual preamp tube. V1 is the tremolo oscillator, which I'm not replacing since I rarely use it.

2b. Even better, does anyone know where the last 6BK11 is hiding?

 

Thanks for any advice you could give to a provisional HOC member, who's still waiting for that FedEx truck to someday show up...

 

Mr B

future Millennium DC owner

[212Mavguy]

Silk Electronics. Please mention Gary from Heber in your note. silkel@burgoyne.com He will be able to help.

[MrB]

Thanks,

 

I'll be sure to mention your name.

 

Mr B

[Spectrum13]

Mr. B As I read this I was playing my 2006 150 into my 1965 Reverbrocket 2 purshased new. Back in 2008 a music dealer had a going out of business sale an I picked up a pair of Electro Harmonix 7951's and replaced the RCA's that came with the amp. (I can't remember if both were original. I know one was replaced at the factory in the late 60's) They sound great. I have not swaped them back in in the last five years to see if I can tell a difference but I would be willing to for an HOC member if asked. These amps are not tough on tubes. The EH sounds great in them.

 

Have you replaced the power cord?

[bolero]

these guys are highly regarded as well

 

http://thetubestore.com/

[MrB]

Thanks for the info, guys.

 

Spectrum,

 

No pressure, try it someday if you're in the mood.

I suspect that unless I replace a lot of other old components, such as worn out caps, the difference in tubes will be minimal.

 

Mr B

[Spectrum13]

MrB

 

Put them old bottles back into the G12R and they have more bite and dynamic range. More presents.The EH are twice as fat as the RCA but look the same inside.

I really need to switch back the new 7591 to be sure.

[Guest HRB853370]

MrB

 

Put them old bottles back into the G12R and they have more bite and dynamic range. More presents.The EH are twice as fat as the RCA but look the same inside.

I really need to switch back the new 7591 to be sure.

 

Hail to the Ampeg King!

[MrB]

Spectrum,

 

Thanks for running the experiment!

More dynamic range...

And they comes with presents? `,:-)

Now you've got me leaning toward shelling out the big bucks...

 

Mr B

[MrB]

I did it,

 

I shelled out for the NOS power tubes.

From KCA NOS Tubes - they seem to have the best prices, and fast service.

And some NOS preamp tubes showed up online.

At Fliptops - that carry lots of Ampeg parts, but are quite pricey.

 

Results:

Much better sound than the 46 year old originals.

And I put in a new Eminence Legend 1258 speaker.

More efficient and brighter (and newer) than the original Ampeg labeled Jensen P12R.

 

One problem that did not resolve:

There is a several minute delay from flipping the power switch to getting the amp to actually amplify.

Sounds to my totally electronically ignorant ears, that perhaps some capacitors need replacing.

Any thoughts?

 

And Spectrum,

I didn't understand why you asked about replacing the power chord, until I noticed something on an online repair shop website, that said they can add a grounded power chord.

Sounds like something I can do myself. I'll assume I attach the third wire to the chassis. But how do I know the correct polarity for the original two wires?

 

Thanks to everyone for your help,

Mr B

[bolero]

did you replace the recifier tube? I seem to recall some of them ( not sure which models ) can take a while to warm up, and get current flowing to the rest of the tubes

[MrB]

Bolero,

 

Good thought, but it has a solid state rectifier.

The tubes all glow nicely when I turn it on.

And it's strange, because it's not just a 30 second delay, but around 2 or 3 minutes...

 

Mr B

[Hfan]

I did it,

 

I shelled out for the NOS power tubes.

From KCA NOS Tubes - they seem to have the best prices, and fast service.

And some NOS preamp tubes showed up online.

At Fliptops - that carry lots of Ampeg parts, but are quite pricey.

 

Results:

Much better sound than the 46 year old originals.

And I put in a new Eminence Legend 1258 speaker.

More efficient and brighter (and newer) than the original Ampeg labeled Jensen P12R.

 

One problem that did not resolve:

There is a several minute delay from flipping the power switch to getting the amp to actually amplify.

Sounds to my totally electronically ignorant ears, that perhaps some capacitors need replacing.

Any thoughts?

 

And Spectrum,

I didn't understand why you asked about replacing the power chord, until I noticed something on an online repair shop website, that said they can add a grounded power chord.

Sounds like something I can do myself. I'll assume I attach the third wire to the chassis. But how do I know the correct polarity for the original two wires?

 

Thanks to everyone for your help,

Mr B

I'm no expert (we hhave some here) but I believe there is no fixed polarity on the original 2 power chord wires as you are dealing with AC (Alternating Current) so polarity continually reverses itself. Think sine wave. Your old wires may be colored black and white, I'd match that with the new one, not sure if you have to but I would. You really should replace the old plug for safetys sake.

[MrB]

Hfan,

 

I think it does make a difference. As you may recall, with the old two-wire chords, plugging in the wrong way gives you a buzz.

(so does playing a guitar through it, standing on a dank basement floor)

Reversing the plug solves that.

Which gives me one solution:

Wire it one way, and if there's buzzing, reverse it.

So much for solving things with rational thinking.

 

Mr B

[Hfan]

I have fuzzy thinking on this, like I said no expert. The old Fender amps had that toggle switch which did the same thing, once you add the 3 prong with the ground it is a non issue. I would do some research, I haven't installed a 3 prong on an old amp in years, think I just matched colors and added the ground to the lug of the power xformer. FWIW, Music electronics forum is great for this sort of stuff, lots of amp experts that help out the cluless or confused.