Jess Oliver's legacy - AMPEG PORTAFLEX CLUB part 9

[Jignant]

Thanks everyone! Used this at practice last night and WOW!!! I had forgotten how great it sounds.

Solid full tonal bliss! For this band application, it is plenty loud for practice so I am going to try miking the cab first at a gig. Today I am going to dig out and reinstall the original tubes. I am quite curious as to what they are...I replaced them in the 90s sometime.

Thanks to my Dad (he is my leader of the band) for such a great vintage piece and thanks to all for your welcome and for the microphone recommendations. My parents are retired music teachers and have supported music and my ongoing gear lust my whole life. I am blessed with more musical equipment than I will ever really need. His last gift was his 1963 Gibson L7c. I wish he would continue to play, but 30 years + as a music teacher kind of put that fire out.

I am looking forward to improving my bass playing skills and learning and contributing here!

[Mr.Fingers]

VERY good experiences with the Electrovoice RE20. The entire album was recorded with it ('62 B15N, with EB2D, Ripper & P-bass), pretty equal frequency response over the whole spectrum.

For this advice, your father may reward me with an ES345, a sunburst if possible

[beans-on-toast]

I've got an ES347. I replaced the pickups with 59 PAF's. Nice sustain and rich beefy tone through a B-15.

[spacebassed]

The fellow i bought my '61 B15 from used it with a '61 ES-175 it's entire life. As far as I know it never had a bass plugged into it before it came to me.

[beans-on-toast]

Jazz guitarists loved the B-15. Maybe that's what your '61 was used for.

[spacebassed]

That was my first thought too, but it turns out he played country/rockabilly through it. I agree though, b15's have a KILLER jazz tone.

[spacebassed]

and David, about jnewmarks B15, we forgot to mention that running 6550's or KT88's in place of the 6l6's could also be something to try. Would the mods you mentioned cause any problems if KT88's were used?

[beans-on-toast]

I think that any mod is worth a try. The mods would be fine with a different power tube.

I've never tried anything other than a 6L6GC in the B-15N. I think it's because I really like the character of the amp with that tube. The 6550A or KT88 would change that and the amp wouldn't sound the same.

There are current capacity issues to consider. Both the 6550A and KT88 require 1.6A for each tube for a total of 3.2A. A 6L6GC requires 0.9A per tube or 1.8A for both. So the they would draw and extra 1.2A. The power transformer on the B-15 tends to run hot as it is with the 6L6GC's. I wouldn't want to push a vintage transformer harder. Now if only the solid state rectifier were used, the amp would be drawing 1.9A less current because the SS module doesn't have a heater like a tube has. This would take the edge off of the larger current draw of the 6550A or KT88 and balance things out but would restrict how the amp could be used. No more tube rectifier.

My other concern is the output transformers capacity. I believe that the original Stancor transformer was rated at 50W max. On a bass amp you want heavy iron and a conservative rating so running it at 25 to 30W was a good match. Depending on the design, a push pull pair of those other tubes could put out as much as 100W. Using them would require some changes to the power supply. Then there are impedance issues to consider between the power tubes and the output transformer.

In the end it would be quite a different amp. It would be interesting to hear how it would sound. Somehow I'm thinking that it wouldn't have that smooth and rich B15 magic.

[Farfetched]

picked up these two last night. haven't cracked them open yet, but apparently both 67s. more pics later....

[christw]

Originally Posted by Farfetched

picked up these two last night. haven't cracked them open yet, but apparently both 67s. more pics later....

Two!?

[spellcaster]

Originally Posted by beans-on-toast

I wouldn't want to push a vintage transformer harder. Now if only the solid state rectifier were used, the amp would be drawing 1.9A less current because the SS module doesn't have a heater like a tube has. This would take the edge off of the larger current draw of the 6550A or KT88 and balance things out but would restrict how the amp could be used. No more tube rectifier.

Would a Weber copper ss rectifier work for this? That could be interesting to play around with since I have some 6550's and a Weber rec on hand.

[spacebassed]

Originally Posted by spellcaster

Would a Weber copper ss rectifier work for this? That could be interesting to play around with since I have some 6550's and a Weber rec on hand.

Yes, the copper cap would not only work, but would be preferable due to the inrush limiter mentioned above. Just remember that you'll need to check/adjust the bias when swapping in the 6550's. If you try it, keep an eye on your transformers, and let us know how it works out!

[Farfetched]

Originally Posted by christw

Two!?

yep. well on my way to hoarding....

[spacebassed]

Originally Posted by beans-on-toast

I think that any mod is worth a try. The mods would be fine with a different power tube.

I've never tried anything other than a 6L6GC in the B-15N. I think it's because I really like the character of the amp with that tube. The 6550A or KT88 would change that and the amp wouldn't sound the same.

There are current capacity issues to consider. Both the 6550A and KT88 require 1.6A for each tube for a total of 3.2A. A 6L6GC requires 0.9A per tube or 1.8A for both. So the they would draw and extra 1.2A. The power transformer on the B-15 tends to run hot as it is with the 6L6GC's. I wouldn't want to push a vintage transformer harder. Now if only the solid state rectifier were used, the amp would be drawing 1.9A less current because the SS module doesn't have a heater like a tube has. This would take the edge off of the larger current draw of the 6550A or KT88 and balance things out but would restrict how the amp could be used. No more tube rectifier.

My other concern is the output transformers capacity. I believe that the original Stancor transformer was rated at 50W max. On a bass amp you want heavy iron and a conservative rating so running it at 25 to 30W was a good match. Depending on the design, a push pull pair of those other tubes could put out as much as 100W. Using them would require some changes to the power supply. Then there are impedance issues to consider between the power tubes and the output transformer.

In the end it would be quite a different amp. It would be interesting to hear how it would sound. Somehow I'm thinking that it wouldn't have that smooth and rich B15 magic.

Thanks David, that's what I was thinking, that using the SS rec would offset the additional heater current draw of the KT88 or 6550's, I just wanted to run it past you first. Don't forget that prior to the 5ar4 the B15 used a 5u4, which draws 3 amps (1.1 amps more than the 5ar4) of heater current.

I think if more power is what jnewmark is looking for this would be something to consider. As far as what to expect tonally, maybe christw can chime in, I know he replaced the 7027a's in his B12xtc with KT88's. I'd definitely be interested in hearing the results myself, with the SS rec, KT88's, a more efficient speaker, and the mods you suggested it seems to me like you could really increase the output - it's worth a shot!

[ddbassGA]

The discussion above has me thinking about trying 6550's in my '64 B18 head w/ factory SS rectification. With cathode bias would I need to even worry about rebiasing?

[christw]

The 6550's in the B-12XT head gave it a huge pillowy bottom underneath with an otherwise similar tonal profile and overall output. I think some of you guys would dig it. It works very well with my upright.

[JimmyM]

#326 lowend81
#327 Jignant

Wessman, sorry...gave you a second number accidentally. So you're no longer 326...you're 289.

Guitar in a B-15? I love it in mine but I prefer the 2nd channel because of the low rolloff. Don't know how it is in others but mine's a 64 NC, so that's what I do to play guitar with it.

[ddbassGA]

Originally Posted by christw

...a huge pillowy bottom...

Sounds like my first wife.

[JimmyM]

Originally Posted by ddbassGA

Sounds like my first wife.

Yeah, it does, doesn't it?

[ddbassGA]

Good one Jimmy!