Resurrection of Point to Point Toob Amp

[OldHack]

Found this in the back shed of a radio shop. It was given to me for the asking when I worked there one summer a few years back. Fuse holder, a tube, and the A/C plug were missing. Cleaned it up and started resurrection today. Plugged it in and lo and behold the pilot light lit up! A few seconds later and we have hum! Plugged in the bass and we have electric bass! Works with the one power amp tube, but has a hellish buzz without any volume on. Sounds quite bright but I couldn't play around with it much; gf says it was loud haha! (it wasn't really but it could get quite annoying for the neighbors, I am sure, judging by the gain). I think I'll try to pick up another 7027A unless someone here has a better idea. I know I've got a couple of new 6L6's kicking around buried deep in storage somewhere...I have no idea if they would fit and what else I'd need to change. It sounds really bright. Anyways, thought it would make a funky practice amp if I can get it going a little better. I just like the look of it sitting next to the couch






Enough inputs for the whole band!


Fuse? We don't need no stinkin' fuse! (I soldered in an automotive in-line holder inside)


Slight overkill with the speaker cable, but hey, I got it cheep as a precut at Home Depot


Just happened across this 1/2" mic to phone plug adapter the other day in a mic case

[johnk_10]

hmmmm. it looks almost exactly like a McGohan M-50 (only it was a two channel amp) that i recently worked on, and it sounded great.

[taurus1]

man that is sweet. I'd build a Hiwatt style head case for that thing, although it looks really cool as is.

[svtb15]

I need to get one of these old babys.. Ill bet they are great to record with... That into a TL606 would be nice.

[OldHack]

I gotta dig around for those 6L6GCs I got somewhere... with a little socket pin reconfig they should be a drop in.

[T-Bird]

Hi.

A great looking amp. Thanks for sharing.

I do have to admit that did think: "oh well, yet another turret board amp that's mistaken for a PTP". To my surprise, it wasn't the case this time .

If I were You, I wouldn't put a fuse inside of the chassis though, especially if the amp is going to see some gig/recording duty. Which it's hopefully going to see.

Regards
Sam

[OldHack]

Originally Posted by T-Bird

If I were You, I wouldn't put a fuse inside of the chassis though, especially if the amp is going to see some gig/recording duty. Which it's hopefully going to see.

Regards
Sam

Thanks, Sam.. sometimes the best things in life are free! Spent a good chunk of the day digging through my storage boxes and no 6L6GC's to be found. Well, actually did find a used GE in a box. (gf was quite intrigued by its total Frankenstein high voltage vibe). Tiny compared to the towering 7027A, but they are supposed to be warmer and fatter sounding which is what this baby needs. I don't want to risk pushing the transformers with 6550's. I still need to make a trip to the parts store for a replacement fuse holder and some ends for the speaker cable too. I want to find those new 6L6GC's dammit! I carried those for years as spares for my D-180 and never needed to use them.

Welcome to my new hobby/obsession.

Cheers

[OldHack]

RCA "BS" Series




Amparex?


Jump in any time if you know what I should be doing. I sure as heck don't

[Bassmec]

Originally Posted by OldHack

RCA "BS" Series




Amparex?


Jump in any time if you know what I should be doing. I sure as heck don't

Change out all the electrolytic's then replace all the crappy ceramic disc caps with metalized polyprop or silver mica.
Drop in a pair of KT 88's and arrange variable fixed bias accordingly.

Best bass amp tubes!.
Thats what you should be doing!.

[BassmanPaul]

Originally Posted by Bassmec

Change out all the electrolytic's then replace all the crappy ceramic disc caps with metalized polyprop or silver mica.
Drop in a pair of KT 88's and arrange variable fixed bias accordingly.:

Good advice except for the KT88 bit. Dropping those in will stress the power transformer for no gain in output power. Why not just install a pair of 7027s. They're readily available nowadays.

Paul

[OldHack]

Thanks for the advice; I'm calling around to see what's available locally. The cheapest way to get this going looks to be a couple of Mesa Boogie 6L6s for $41 CDN a pair. Still phoning around. There's a local flea market vendor I want to check out tomorrow. I was also advised to change the filter. I think it's this dynamite stick looking piece:



Edit: Checked the power tube socket pin config, it's the same for 6L6's so I fired it up for a short time with the mismatched toobs. Much less hum, drowned out with quiet playing. Lots of overdriven sound available and some power, too. Could move the speaker with light muted tapping on the E string even at < 1/4 volume. The quest for the missing 6L6GCs continues...

[JimmyM]

ya, that's the filter cap. if you're having problems with hum it might not be a bad idea, but it looks to be in pretty good shape other than just being old. just remember to discharge it fully before futzing with it.

[KramerBassFan]

Cool!

I'd do it right, and just get some new 7027's.

Just be glad it isn't asking for say, 8417's

[RickBlair]

You might want to try to find out what the input impedance is on the mic inputs. Generally, plugging a bass into a mic input doesn't result in a great sound. You could try running the output of a preamp into the line in input to see what kind of sound you get also.

Rick B.

[thumpbass1]

Sweeeeeeeeet! I love funky old tube p.a. and hi-fi amps. They can make for some fun projects. Congrats on your find. I'm definitely drooling over those old Amperex branded 12AX7's you got there.

[Bassmec]

Originally Posted by BassmanPaul

Good advice except for the KT88 bit. Dropping those in will stress the power transformer for no gain in output power. Why not just install a pair of 7027s. They're readily available nowadays.

Paul

http://www.triodeel.com/7027.htm
Quote:
Q.Sob! 6550 or EL 34 can't be installed in my Bogen/Musak/whatever, like in an Ampeg??

A. Maybe. I cannot confirm that power transformers in those units can handle the extra load. You can try installing the 6550, KT88, etc, in your amp, (remember for EL34, a jumper should be installed between pins 1 & 8) adjust bias for the same idle current (typically 40 or 50 ma) as a 7027, then checking B+/HT and filament voltage. If it's way down (say the fil line is reading less than 6.2 volts)...no go. Put the 6L6-GC's back in...

I think the mains transformer in the original posters amp looks a sturdy unit I would be very tempted to give it a go running KT88's maybe for hardly any real gain in watts but for late breakup and really great tone.

[Eight_Stringer]

Educated guess, that orange cappy was manufactured 23rd week of 1960. It is only 50 years old! FWIW, swapping output tubes is dependant on the impedence ratio of the output tranny as much, or more so, than the nominal power handling variance ( further reading, on plate loads for the interested ). Love the input/mic connectors, forgot all about those.... Regards.

[OldHack]

Originally Posted by RickBlair

You might want to try to find out what the input impedance is on the mic inputs. Generally, plugging a bass into a mic input doesn't result in a great sound. You could try running the output of a preamp into the line in input to see what kind of sound you get also.

Rick B.

OK, fed the B**ringer into the phono input:





Great piece of advice! With my active basses this is really sounding like the smooth ol toobey it is now!

Thanks Rick and all

Cheers!

[KramerBassFan]

Originally Posted by Eight_Stringer

Educated guess, that orange cappy was manufactured 23rd week of 1960. It is only 50 years old! FWIW, swapping output tubes is dependant on the impedence ratio of the output tranny as much, or more so, than the nominal power handling variance ( further reading, on plate loads for the interested ). Love the input/mic connectors, forgot all about those.... Regards.

Or on the 240th day of 1969.

That said, i don't really know codes by memory.

[Eight_Stringer]

Originally Posted by KramerBassFan

Or on the 240th day of 1969.

That said, i don't really know codes by memory.

Looking at the rest of the under chassis shot, think your closer than me to the actual date. Feeding that capy are solid state rectifiers ( again best guess, doubt if these diodes are a flyback string ) Being SS diodes that would put it post early 60's, with the Spraugue or Philips blue electro's would say late 60's like you indicate. Main HT filter capy is above chassis would think, as this orange one is low uF.. maybe a capy for the front end tubes HT? 400V is high for that...dunno.... get anycloser will stick my nose on a HT spot, as the eyes are all but shot.... Regards.