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Topic: Question for tube amp techs |
Dave Zirbel
From:
Sebastopol, CA USA
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Posted 31 Oct 2019 5:59 pm |
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Hi folks. I’ve been playing through an old Newcomb Pathfinder E-70 PA head lately. 70 watts. It’s been modded for electric string instruments and sounds amazing. It’s powered by two 7027a tubes and pretty sure it has an SS rectifier. It also has a 6v6 tube plus 12ax7a preamp tubes.
Just curious what the 6v6 might be in there for...seems unique to me but I’m not a tech.
Thanks
Dave
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Dave Zirbel-
Sierra S-10 (Built by Ross Shafer),ZB, Fender 400 guitars, various tube and SS amps |
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Eric Philippsen
From:
Central Florida USA
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Posted 1 Nov 2019 3:29 am
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| Off the top of my head, without looking at it or it’s schematic, it might function as a voltage regulator. |
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Jack Stoner
From:
Kansas City, MO
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Posted 1 Nov 2019 5:17 am
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The 6V6 is used as a power output tube, sort of a low power 6L6. Some old Fender amps used 6V6(s) for power output tubes.
Can't say what that is used for without a schematic. I can't find a schematic, but many of he Newcomb's use 6V6's as the power output tubes. |
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Greg Cutshaw
From:
Corry, PA, USA
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Greg Cutshaw
From:
Corry, PA, USA
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Bill Sinclair
From:
Waynesboro, PA, USA
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Posted 1 Nov 2019 5:55 am
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Greg,
Did you read that thread? I had to stop so my blood pressure would go back down.  I'm not sure that I have the patience that some of the helpers on that website exhibited. |
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Dave Zirbel
From:
Sebastopol, CA USA
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Posted 1 Nov 2019 6:43 am
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Thanks guys. Interesting stuff. This amp is really clear but warm sounding and fills the room without hurting anyone ðŸ‘now to find a good pair of 7027’s as a backup!
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Dave Zirbel-
Sierra S-10 (Built by Ross Shafer),ZB, Fender 400 guitars, various tube and SS amps |
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Michael Brebes
From:
Northridge CA
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Posted 1 Nov 2019 8:50 am
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Per that schematic, the 6V6 is used for dropping the 600VDC down to 400VDC to set up the correct grid biasing of the 7027 power tubes and to get the voltage down for use by the preamp tubes.
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Michael Brebes
Instrument/amp/ pickup repair
MSA D10 Classic/Rickenbacher B6/
Dickerson MOTS/Dobro D32 Hawaiian/
Goldtone Paul Beard Reso
Mesa Boogie Studio Pre/Hafler 3000
RP1/MPX100 |
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Ian Worley
From:
Sacramento, CA
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Dave Zirbel
From:
Sebastopol, CA USA
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Posted 1 Nov 2019 9:35 am
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| Quote: |
| This discussion on Audiokarma suggests 6L6GC is a suitable substitute for a 7027A, and easier to come by for a reasonable price: |
Yes but I think the pins (or just one pin) needs to be rewired to make them work. Yes?
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Dave Zirbel-
Sierra S-10 (Built by Ross Shafer),ZB, Fender 400 guitars, various tube and SS amps |
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Greg Cutshaw
From:
Corry, PA, USA
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Tim Marcus
From:
San Francisco, CA
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Posted 1 Nov 2019 1:41 pm
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Thats interesting - I have seen a 6L6 voltage regulator but never a 6V6 like that.
Its dumping about 200v so that the plates of the output tubes can run at 600v and then the next stage of the power supply picks up at 400V (screen supply)
Cool!
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Milkmansound.com |
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Dave Zirbel
From:
Sebastopol, CA USA
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Posted 2 Nov 2019 6:17 am
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Well I played two gigs with this amp yesterday and it blew in the first set of the second gig🙠back to the shop. Kinda funny because one of my musician friends came up to the stage to see what I was playing through at the exact moment it blew😂he wanted to see what that awesome sounding amp was that I was playing through
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Dave Zirbel-
Sierra S-10 (Built by Ross Shafer),ZB, Fender 400 guitars, various tube and SS amps |
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Dave Zirbel
From:
Sebastopol, CA USA
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Posted 2 Nov 2019 12:47 pm
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Blown fuse...easy fixðŸ‘
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Dave Zirbel-
Sierra S-10 (Built by Ross Shafer),ZB, Fender 400 guitars, various tube and SS amps |
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Len Amaral
From:
Rehoboth,MA 02769
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Posted 2 Nov 2019 1:22 pm
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Greg, you are a wealth of technical information. Bravo!
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I survived the sixties! |
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Stephen Cowell
From:
Round Rock, Texas, USA
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Posted 9 Nov 2019 4:24 pm
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| Dave Zirbel wrote: |
| Blown fuse...easy fix👠|
Blown fuses normally indicate other problems... keep a close watch on the 7027's, if they get red hot ('cherry up') you'll need to have them biased (changing a resistor on this amp). Nice amp, good luck.
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New FB Page: Lap Steel Licks And Stuff: https://www.facebook.com/groups/195394851800329 |
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Dave Zirbel
From:
Sebastopol, CA USA
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Posted 10 Nov 2019 7:47 am
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| Quote: |
| Blown fuses normally indicate other problems... |
Yes. The tubes really don't run abnormally hot. When the fuse blew my friend who was there said his '64 Deluxe blew in "that same corner" of the stage. It's a 100 year old building and sounds like the wiring and power might be sketchy. Also when I replaced the fuse it had a 5 amp fuse when the schematic called for a 3 amp fuse.....would that cause it to blow?
I drove it hard yesterday at an outdoor gig and use my Furman power conditioner/surge protector....no problems and sounded great.
As long as I'm using "antique" gear I'll be bringing backup!
Thanks everyone for the input!
dave
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Dave Zirbel-
Sierra S-10 (Built by Ross Shafer),ZB, Fender 400 guitars, various tube and SS amps |
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Steve Waltz
From:
USA
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Posted 12 Nov 2019 9:28 am
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Dave, I think the use of a higher rated fuse is a bad idea as it might not blow when it should and might hurt other parts. The 5 amp fuse could have been been used because something was blowing the proper fuse. It's likely that something isn't right in your amp.
I'm not sure the replace only what shows obvious signs of an issue method of a local repair guy is the best method for someone that needs a very reliable amp? It's a bit of a drive to get it repaired every time something goes wrong when some of those parts could be replaced before an issue, considering the age.
My limited experience makes me think tone is in the circuit not some mojo of old resistors and capacitors. |
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Dave Zirbel
From:
Sebastopol, CA USA
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Posted 12 Nov 2019 9:38 am
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Hi Steve. What I was saying is the fuse that blew was not the one the schematic called for. I put in the proper fuse.
Not sure where the mojo comes from either but this thing sounds great, and I'm not the only one that thinks so! 
I played it hard last weekend for two hours outdoors with no mic on the amp....no problems, but I will continue bring backup.
Where are you hiding out? Haven't seen you forever!
Dave
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Dave Zirbel-
Sierra S-10 (Built by Ross Shafer),ZB, Fender 400 guitars, various tube and SS amps |
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Dave Mudgett
From:
Central Pennsylvania and Gallatin, Tennessee
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Posted 12 Nov 2019 10:13 am
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Unless there was something wrong with the 5A fuse, putting it in place of a 3A fuse would not cause it to blow. Quite the contrary, putting in a 5A fuse could cause it not to blow when it should. I see this a lot on other peoples' amps - someone will have a problem with the correct-rating fuse blowing and install a higher-rating fuse. This is a recipe for disaster, and a tip when buying an amp that there is a problem.
There could be something besides a red-plating tube causing a fuse to blow. So many possibilities. Unless you're handy with tube amps, I'd get it to someone to check it out. Cool amp. I love old tube Hi-Fi and PA amps. |
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Dave Zirbel
From:
Sebastopol, CA USA
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Posted 12 Nov 2019 10:32 am
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| Quote: |
| There could be something besides a red-plating tube causing a fuse to blow. So many possibilities. |
Earlier in this thread I said that my friend who there when it blew said his '64 Deluxe blew in the exact same corner of the stage I was on.....could it be the fact that the building is 100 years old with a sketchy power source?
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Dave Zirbel-
Sierra S-10 (Built by Ross Shafer),ZB, Fender 400 guitars, various tube and SS amps |
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Dave Mudgett
From:
Central Pennsylvania and Gallatin, Tennessee
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Posted 12 Nov 2019 10:50 am
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Certainly possible that bad power could cause an amp to blow. That's why I use the Furman AR-1215 voltage regulator I discussed on your other thread about power conditioners.
But I wouldn't assume that's the issue. Unless it's been gone over recently by someone you trust, I think a 60-year old tube amp is definitely due for a service check.  |
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Dave Zirbel
From:
Sebastopol, CA USA
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Posted 12 Nov 2019 10:59 am
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| Quote: |
| Unless it's been gone over recently by someone you trust, I think a 60-year old tube amp is definitely due for a service check. Wink |
Yeah probably wouldn't hurt. I believe this rig was set up and modded for guitar about 10-15 years ago. It blew once in my basement and my friend that works for Mesa Boogie said he replaced a few resisters and a preamp tube.....the old fuse that I replaced looked ancient...the tech that set it up moved a little farther away but it may be time to do a tune up!
Thanks guys
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Dave Zirbel-
Sierra S-10 (Built by Ross Shafer),ZB, Fender 400 guitars, various tube and SS amps |
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Steve Waltz
From:
USA
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Posted 12 Nov 2019 11:00 am
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Dave,
I was splitting guitar work with the Alcatraz Islanders and that kept me busy enough but that weekly gig ended and I've been busy with non music stuff.
I believe in amp Mojo. So I'm sure yours has that. My mid 50's Sano has it, had it, and still has it even after a ton of parts were replaced. Because I replaced so many parts, I think it's as reliable as a new amp and the overall tone didn't change. I've just seen a few local amps that were worked on and the original caps were still in it from the 50's when those could be replaced at no cost to mojo and only add reliability.... In my opinion.
You might want to check the multi section can capacitor. The 10/35/10/40. Someone might have put new single ones under the chassis. At least those would be new. If they aren't there and the cap is old, that would be a good thing to replace. You can get something like the original at around $40 for parts or mount under for cheaper. |
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Dave Zirbel
From:
Sebastopol, CA USA
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Posted 16 Nov 2019 12:19 pm
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Well go ahead and say “I told you so!â€ðŸ™„ The amp blew again even with my
power conditioner at a legit venue. Back to the shop. Good thing I carry backup!
Thanks everyone ðŸ™
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Dave Zirbel-
Sierra S-10 (Built by Ross Shafer),ZB, Fender 400 guitars, various tube and SS amps |
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