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Discussion in 'Glowing Bottle Tube Amp Forum' started by Phrygian77, Feb 22, 2020.
Wow! Nice piece of history you got there. How does it sound? What tubes does it have in it? What speaker is that? How many watts?
Wow. Got a nice speaker upgrade along the way. Did you just acquire this? If so, congrats!
It's on my bench for a check up. I haven't even fired it up yet. Supposedly, Gerald Weber worked on this amp at some point. The JBL is a D130F.
What's the story?
I see you posted the story while I was typing...
That's hilarious because I was about to say that it looks like it fell into some hands that probably didnt have any business messing with it based on the shotgunning of orange drops in place of all the vintage coupling caps...
Are you just giving it a check up or are you going to make any changes?
I'd be strongly urging the owner to at least spend the money to put the correct preamp tubes back instead of those converters. I'd also get something other than that JBL in there, that seems like a really weird match for that amp, but who knows maybe it sounds great?
Yeah, it's some ugly work ... tack soldered caps, most of the original wiring replaced. The '47 Dual Professional he brought to me was in much better shape. It just needed a little DeoxIT, and it had a microphonic preamp tube. That one had converters in it too, 6SJ7 to EF86. The JBL in this was originally a 16 ohm, but it's been reconed apparently to 8 ohm. He has a JBL in his '56 Vibrolux, so I know he likes them, but he was also talking about swapping that for an original Jensen.
This is both the '48 Pro and the '47 Dual Professional on stage at 0:11...
When he takes the cover off you see how clean it is. Original OT on the speaker.
I didn't even know they made them back then, I thought 53 or so... I had a 54 Bassman that was very similar. But had brown vinyl somewhat like the vinyl on that one.
At what point is it no longer a 1948 pro? New tubes, new caps, new speaker...
Wow. And with a JBL. And is that a potato-masher Bendix rectifier tube?
Great store. Very close to my house and always a pleasure to see what’s there.
It's a JAN 5R4. This amp is drawing .8A at the wall, so I suspect the tubes are running really hot. I haven't measured the bias yet. I think the 5R4 has more voltage drop. A 5U4GB would probably be too much (voltage, that is).
Well, I don't agree with what was done inside this amp, but consider that even if it were 100% original with all components working perfectly, it's still not the same amp as it was in 1948 because of the increased line voltage. That increase in plate voltage certainly has an effect on the tone. Honestly, the JBL doesn't sound as bad as I thought it would with the gain. I liked the Jensen C10Qs reissues in his '47 better. The 12AX7s have a bit more gain than 6SC7s, but that's not really a bad thing.
Here's my '49 with an original-cone '53 Jensen P15N; 1 GE & 2 RCA 6SC7 (metal); matched 50's JAN-CHY-6L6WGB; and an RCA 5U4.
The tweed's missing off both sides and the bottom but it SOUNDS so darned good I don't care. A vintage broker I work with bought it to use in his studio & automatically installed a newer, higher-sensitivity Weber speaker figuring he'd need it for headroom. He didn't like it and sold it to me with the Jensen for peanuts.
And it actually has MORE headroom and output with the Jensen. Go figure!
I need to do a cap job on it (I don't trust the 15 year old Atoms at all - replaced too many blown ones) I do wish all the tone and coupling caps hadn't been replaced, but at least it's quality work & they used Jupiter caps. If the '53 Jensen was the original speaker I'd call Thom and order a Tone Tubby to use & store the original - but since the '53 isn't the original speaker - and I have ANOTHER one - I'd rather use it as-is! So it's wired up in "the buffet" area (named by my late son, David) with my primary guitars, effects and all my blonde amps!
Plate to cathode is 405VDC with 50mA plate current.
I'd say after those things. Those are maintenance. Now trannies, cab etc... Although the speaker is on the edge, plenty of old P15N's are available, albeit mostly unusable really...
You reminded me, I need to put the tuners and bridge on a tenor sized six string uke I built. I probably will not get to it today but I am just about finished another project and it can then sit in the top tier of my to-do list.
The joy and sadness of being an amp tech haha. We get to babysit.