• TalkBass has been independent since 1998. Add your voice.
    Create a free account to reply to discussions, view embedded media, and browse with fewer display ads.
    Join free Log in
    Want zero display ads or expanded classifieds tools? Compare plans.

6550's in a B-15

#21
BassmanPaul said:
I'm not so sure this is true. Each pair of 6550 is going to require getting on for one and half amps more in heater current. That's an added load of about 9VA the power transformer has to supply over what it was designed for. It will run hotter and have a shorter life. The PT in my B15 certainly runs warm enough already.

Paul
Click to expand...
Thank you for posting these words of wisdom. I would not want to place the power transformer in a vintage B-15 under any more stress than it already is. Many B-15's have suffered burned-out power transformers over the years just from more-or-less normal use, and adding the extra load of the 6550 heaters is not doing the amp any favor. I would also recommend installing a Weber Copper Cap rectifier in a B-15 to get rid of the tube rectifier filament, putting less stress on the PT. ("The Copper Cap emulates a tube rectifier, but it does not require filament power. In the case of a 5U4, for instance, this is a savings of 15 watts. The power transformer will run cooler and last longer.")
 
#22
robgrow said:
Thank you for posting these words of wisdom. I would not want to place the power transformer in a vintage B-15 under any more stress than it already is. Many B-15's have suffered burned-out power transformers over the years just from more-or-less normal use, and adding the extra load of the 6550 heaters is not doing the amp any favor. I would also recommend installing a Weber Copper Cap rectifier in a B-15 to get rid of the tube rectifier filament, putting less stress on the PT.
Click to expand...
That's half the fun of the B-15, dude...that's what you call "warm tones" ;)
 
#23
Yo Jimmy M....How ya doin"? Hope all is well. I have an all original, working 1966 B-18N with the original 7027's (that say Ampeg on them) still in it.
I looked up 7027's and found this little quip from Torres Engineering. You might be interseted. I believe the 7027's that were used in the old Ampegs were a JAN tube and made to last a long time as well as sound good. JAN stands for Joint/Army/Navy... )-(
[Invalid or Expired Link Removed]
 
#24
would it not be possible to fit the straight bottle 6550's? i have a GT branded 6550 that was in an old wasp (australian amp from the 70's). it is a straight bottle that doesn't bubble out like many. i think sovtek 6550's are that size.

i dont know anything about the circuitry/layout/transformers of the amp, and cant look now, but it doesnt seem out of the question.
 
#25
doktorfeelgood said:
Yo Jimmy M....How ya doin"? Hope all is well. I have an all original, working 1966 B-18N with the original 7027's (that say Ampeg on them) still in it.
I looked up 7027's and found this little quip from Torres Engineering. You might be interseted. I believe the 7027's that were used in the old Ampegs were a JAN tube and made to last a long time as well as sound good. JAN stands for Joint/Army/Navy... )-(
[Invalid or Expired Link Removed]
Click to expand...
Hey Dok! That's quite a fliptop. And quite a testament to the quality of tubes back then.
 
#29
Problem I have found is that manufacturers of tube amps meant for musical instrument use very often use iron that is too small and therefore marginal for the intended application. Remember when some of these amps were designed volume levels were nothing like what they are today. Add to that the use of all sorts of effects and things get worse.

Paul
 
#30
Wild. Never was the type to abuse gear myself. Well OK, I have abused gear before, but not to that extent to where I blow a transformer. Rob, I'm sure we would all be entertained by the story behind that.
 
#31
hmm okay then, maybe it's be wiser to leave well enough alone and go with some stout fat sounding 6L6's instead. in a portaflex chassis i don't see how there'd be any extra room to install an auxillary filament tranny. besides you'd ruin the resale value of the amp. in my searches i see the JJ is considered to be a great bass application 6L6 and that's what i'm going with with the oliver. and copper caps are really great, i swear by them and they have the advantage of giving the power trannie a break too since they don't draw any heater current. i suppose my buddy is maybe flirting in the danger zone but damn it sounds good...
 
#33
coreyfyfe said:
Actually my tech told me it's fairly common in the older amps because of the wax potting. He said it doesn't allow as much heat dissipation as an open transformer would and causes progressive heat damage, especially when the amp is used for long periods and high volumes, etc.
Click to expand...

Yes exactly.

A potted transformer is supposed to dissipate heat more efficiently than an open transformer. It also helps eliminate buzzing and arcing. The potting material is a much better conductor of heat than air. For best results, the transformer should be potted under a negative pressure to help ensure that the air bubbles are removed. If they aren't, local hot spots around the windings occur, the coating on the wires breaks down, and eventually this leads to a failure as you said. I've seen some Ampeg transformers that appear to have shorted in this way. These amps were designed to operate at 117V. It varies but some areas have 125VAC on the wall plugs now. This, coupled with cranking the amp up too much puts extra stress on an old transformer.

I'm amazed by how many B-15's I've seen with replaced power transformers. A lot of the replacement transformers that I've seen on B-15's have been made by Heyboer Transformers. They seem to have a good track record.
 
#34
Funny...before Jess Oliver replaced it with one he made, my 64 had been dropped directly on the power transformer, and it was all bent in and looked like it had no right to work, yet it worked perfectly and it was only replaced because of looks. I guess I've been lucky with transformers after hearing all this. Never ever had one go down on me.
 
#35
black_labb said:
would it not be possible to fit the straight bottle 6550's? i have a GT branded 6550 that was in an old wasp (australian amp from the 70's). it is a straight bottle that doesn't bubble out like many. i think sovtek 6550's are that size.

i dont know anything about the circuitry/layout/transformers of the amp, and cant look now, but it doesnt seem out of the question.
Click to expand...


Hey! Wasp, had a 50Watt head 2 by 6CA7's ( EL34's ) and it melted the wax poting mix at the better gigs, ton of fun. BLack _Labb, are any wasps still around?

No big deal rewinding a failed power transformer if required, a poted item is a lot more work, however it is possible to rewind.
Output tranny is a little more difficult, depends on interleaved winding layout. Love this techie topic.
Regards.
 
#37
since the topic of 7027A's came up; I've had/have a couple of early '70s Ampegs that came with 7027As, and my tech helped me shed some light on the issue of swapping in 6L6GCs. As far as we can tell, it boils down to this: If you look at a 7027A and a 6L6GC side by side, you'll notice that the 7027 has all 8 pins, and the 6L6 has just 6 (spots 1 and 6 are missing from the 6L6). If you look inside you amp, and your tube socket has no wires coming from pins 1 and 6, it should be safe to run 6L6GCs (but check with your tech to make sure). If no wires are connected to 1 and 6, the amp is using the "6L6 portion" of the a 7027.
Of course, always check bias when swapping tubes....
 
#38
Eight_Stringer said:
Hey! Wasp, had a 50Watt head 2 by 6CA7's ( EL34's ) and it melted the wax poting mix at the better gigs, ton of fun. BLack _Labb, are any wasps still around?

No big deal rewinding a failed power transformer if required, a poted item is a lot more work, however it is possible to rewind.
Output tranny is a little more difficult, depends on interleaved winding layout. Love this techie topic.
Regards.
Click to expand...

i've got 2 200w wasps (one XL (for guitar) and one VBL (Vocals Bass Lead (guitar), basically an all purpose amp) they're great. there are some around. there's a wasp club here that i started, use to search to find it.
 

Latest posts

Top Bottom
Back