Tech: Vacuum Tubes for Fender Champ amplifiers

Subject: Tech: Vacuum Tubes for amplifiers
From: Joe Offer
Date: 30 Aug 11 - 09:29 PM

I have a Fender "Champ" guitar amp that I'm supposed to refurbish and sell for the women's center where I do volunteer work - in working condition, it's supposed to be worth several hundred dollars. It worked fine until a few months ago, and then just went dead. I suspect that one of the three vacuum tubes went out.
In the old days, I'd take the tubes down to the drugstore and test them. Alas, nowadays not even Radio Shack has tube testers. I'm trying to avoid an expensive trip to an audio repair shop. Any suggestions?

By the way, I found a great Website titled http://myfenderchamp.com/.

-Joe-

Subject: RE: Tech: Vacuum Tubes for amplifiers
From: GUEST,999
Date: 30 Aug 11 - 09:36 PM

Try calling Fender and see if they will test them for you, Joe. Tell them what it's about and other than postage, they just might do it for nothing.

Alternatively, see if there is a luthier who works on electric stuff. S/he might have a tube tester.

Subject: RE: Tech: Vacuum Tubes for Fender Champ amplifiers
From: GUEST
Date: 30 Aug 11 - 09:55 PM

Fender Corporate Headquarters
8860 E. Chaparral Road, Suite 100
Scottsdale, Ariz. 85250
Telephone: [phone]
Fax: [phone]
www.fender.com

Subject: RE: Tech: Vacuum Tubes for Fender Champ amplifiers
From: GUEST,punkfolkrocker
Date: 30 Aug 11 - 10:17 PM

simplest and most cost effective option is to just buy a new set of pre-tested valves from a good ebay seller,
and swap them out one at a time..

If it still won't work, then you know you have a trickier problem to deal with.

But fortunately a non working fixable 'classic' amp will still attract fairly keen bidding on ebay.

Subject: RE: Tech: Vacuum Tubes for Fender Champ amplifiers
From: Joe Offer
Date: 31 Aug 11 - 01:40 AM

Punkfolkrocker, it has been years since I heard the term "valves" used to refer to what we call "tubes." Thanks for the memories, I guess.

I'm taking a number from the speaker to guess that this Champ is from 1979. I can't find a serial number or a number stamped on the tube chart, but there is a number stamped on the speaker - so I used this Speaker Code Chart. 4657934 is the number, and I gather that "79" is the year of manufacture. The one I have looks exactly like this one, which has a high bid of $202 the day before the auction ends. This one looks the same, and had a "buy it now" price of $505.

-Joe-

Subject: RE: Tech: Vacuum Tubes for Fender Champ amplifiers
From: Richard Bridge
Date: 31 Aug 11 - 03:20 AM

They are still "valves" in the UK. When you can get them!

Subject: RE: Tech: Vacuum Tubes for Fender Champ amplifiers
From: JohnInKansas
Date: 31 Aug 11 - 04:14 AM

Joe -

Email Sent. (It got out of my send box, but it is kinda large)

Attachment: RCA Receiving Tube Manual 1960, 3 pages on Electron Tube Testing. 2.94 MB PDF.

A clever guy like you ought'a be able to roll your own tester if you're really desperate; but some of the components might be a bit tough to find on short notice.

The whole book is about 318.5 MB. I'd have sent it if I thought it would go as an attachment, but my email usually craps at about 5 MB for attachments.

If you need specs on a few particular tubes, I've got it broken down into nibbles, but all the pieces would require 30 emails to get it all out of my outbox.

John

Subject: RE: Tech: Vacuum Tubes for Fender Champ amplifiers
From: JohnInKansas
Date: 31 Aug 11 - 07:18 AM

In case you haven't found it:

Parent page for:

Fender Champ 5C-1 schematic

and:

Fender Champ 5C-1 layout

If this is the right model, the tubes are:

6SJ7, 6V6-GT, 5Y3-GT (from the layout - The schematic omits both "-GT" bits)

A 5Y3-G that's probably an "early -GT" is shown as obsolete/discontinued (in 1960) but the successor 5Y3-GT was still good "back then."

Note: Both diagrams show a 2A fuse - surely you checked it first?

The layout shows some other component values, if you don't have something better for reference.

John

Subject: RE: Tech: Vacuum Tubes for Fender Champ amplifiers
From: ripov
Date: 31 Aug 11 - 07:43 AM

G and GT just refer to the shape of the glass, G is tapered with a blobby top and GT is straight sided. The works are identical,
Have you checked the valve heaters are alight?
I've no experience of Fender kit, but in valve amps the most likely one to blow is the rectifier 5Y3, followed by the 6V6 output valve. Rarely is it a 6J7

The heater of the 5Y3 has a different supply (5v)to the 6- series valves (6.3v), so if none are alight (a red glow down the centre, not always easy to spot if the glass is greyed on the inside) look elsewhere for the problem!

Subject: RE: Tech: Vacuum Tubes for Fender Champ amplifiers
From: GUEST,punkfolkrocker
Date: 31 Aug 11 - 09:11 AM

yes they'e still called 'Valve Amps' over here..

.. and the last few years has seen a popular resurgence in affordable good quality Chinese manufactured low wattage amps
inspired by the classic Champ schematic..

Supply of new valves is also better than it has been for a long time.
Slovakian JJ valves are highly regarded and inexpensive replacements,
But China is also radically improving it's reputation for quality reliable valves.

I've been trying to find a link for a specialist USA seller well known on amp forums for his expert knowledge
and mail order 'tube' shop.
For the moment I can't remember his name,
though entering 'amp tube seller USA' on google provides many reasonable similar links

Such sellers can be relied on to provide exact rigourlesly pre-tested retubing kits
for specific amps
using modern equivalents [or NOS stock for anyone rich enough]

It sounds like the champ you're refurbishing could probly do with a new set of valves by now anyway....

Subject: RE: Tech: Vacuum Tubes for Fender Champ amplifiers
From: pavane
Date: 31 Aug 11 - 05:43 PM

When I had an old valve radio to fix many years ago, and I couldn't get a new rectifier valve/tube, I just used silicon diodes of suitable rating.
Just a problem that they were more efficient, and the HT (Voltage) was too high - but you could probably find a way to reduce it if so.

Subject: RE: Tech: Vacuum Tubes for Fender Champ amplifiers
From: Joe Offer
Date: 31 Aug 11 - 09:00 PM

Thanks for all your help. A very generous Mudcatter who lives not far from me has worked of Fender Champ amplifiers for thirty years. I'm going to ship the amp to him, and he's going to fix and sell the amplifier for the women's center.
I tell you, Mudcatters are nice people.

-Joe-

Subject: RE: Tech: Vacuum Tubes for Fender Champ amplifiers
From: GUEST,999
Date: 31 Aug 11 - 09:14 PM

Good news. Thanks for sayin' Joe. Sometimes these threads are like response calls: ya think ya did good, but no one ever tells ya ya DID good. I hope it raises some serious coin for the shelter.

Subject: RE: Tech: Vacuum Tubes for Fender Champ amplifiers
From: Bonzo3legs
Date: 01 Sep 11 - 05:23 AM

It might turn out to be the power supply, dead electolytic capacitors for instance - which at the point of failure may well have blown one or more of the valves.

I remember my old Selmer Selectortone amp failing during a gig in the 60s, so I plgged into a spare input on the other guitarist's Ampeg. The guy running the gig offered to check out my amp during the interval as he built radios and had his meter with him. Not only that, he located the dead valve and had a replacement at home which was close by, and my amp was up and running - louder than before!!!

Subject: RE: Tech: Vacuum Tubes for Fender Champ amplifiers
From: JohnInKansas
Date: 01 Sep 11 - 06:02 AM

A contrast in a lot more than just the equipment itself:

When stuff was assembled out of components, you could fix 'em yourself, and the original builder could swap a couple or add one or two or leave some out the build a whole line of things to suit exactly what each customer wanted.

With everything integrated and modularized, its incredibly expensive to make one of anything, and about the same cost to the mfr to make 100,000 of them, as long as they're all alike. As a result WE ARE ALL REQUIRED TO TAKE THE SAME THING, no choices, and no repairs. When it fails we have to take exactly the one replacement that's been made most popular by the mfr's propaganda (call it advertising only if it helps to keep you from puking).

And instead of giving us specs and performance information, all they'll say is "you'll really like this 'cause everybody else has one." "And we can make it any color you want as long as it's red or black."

So we all line up and march up the ramp to the slaughterhouse like good little heifers, because THERE'S NO OTHER CHOICE.

Sorry for the rant, but I guess I miss some things about the good old days - especially some that came before most here had a chance to know anything about them. I suppose we old fossils (I'm not the only one here) should try to be gentle with the youngsters who never had a chance to know... .

John

Subject: RE: Tech: Vacuum Tubes for Fender Champ amplifiers
From: Richard Bridge
Date: 01 Sep 11 - 07:37 AM

Wholly agreed, JiK

Subject: RE: Tech: Vacuum Tubes for Fender Champ amplifiers
From: cooperman
Date: 01 Sep 11 - 08:22 AM

Interesting (and annoying 'cos it happened to me!) modern tube amps are more likely to fail in the circuitry than old ones. The heat from the tubes dries out the tiny solder joints on the PCBs that they mostly now use. The old amps had discrete components that were wound round posts then soldered. Much better in this application!!

Subject: RE: Tech: Vacuum Tubes for Fender Champ amplifiers
From: Mavis Enderby
Date: 01 Sep 11 - 11:02 AM

Glad your Champ is getting fixed Joe. Lovely sounding amps.

I agree with the comments regarding discrete components and tag-strip or turret board construction. Completely appropriate technology and a joy to repair (and make!).

However, integrated and modularised construction isn't all bad in the right place. It would be hard to post to Mudcat from a valve/tube computer, i.e. Colossus or ENIAC

Pete

Subject: RE: Tech: Vacuum Tubes for Fender Champ amplifiers
From: JohnInKansas
Date: 01 Sep 11 - 02:13 PM

WARNING: Soapbox on stage:

Nostalgia isn't about what's better or what's worse. It's about how it affected you and how you remember it. Given the capriciousness of human memory, it's good to understand why "Nostalgia ain't what it used to be."

In about 1959, roughly 25 years after the public appearance of ENIAC, the Dean of the EE Department lectured my class of ME students on the problem that "transistors can't switch as fast as tubes, and can't be used in a practical computing machine." He was telling us what the problem was. (It's likely the majority missed the point.) Quite possibly a few of us who got it may have helped with the solution. I didn't happen to go that direction.

Roughly 1970, 35 years after ENIAC went public, I got my first "hands-on" with an "electronic calculator." It was about the size of an executive desk, and we were told it cost $18,000. About 1K of "ring & wire" memory. It could add, subtract, multiply, divide, and "look up" a limited range of trig functions, and could store ONE "memory constant." It was good for "8 decimal places" (mostly) but only about 5 places were reliably accurate. I had to go back to the office around midnight to get to use it for a couple of hours at a time. All manual input, and I used printed log and trig tables to "correct" most of it's "look-ups."

Around 1979, one of my first assignments at EAC was to decide whether an ejection seat would clear the tail (a rather large one) on the airplane if someone used it. The "trajectory problem" was exactly what ENIAC was built to solve more than 45 years earlier. I ran the numbers on my personal brand new "five function calculator" that I bought for $125 down at Sears Roebuck specifically for the assignment. It had exactly the same functional capability as the $18,000 one I'd used "back in 1970," except that the "lookup trig functions, and the calculations, were actually accurate to the 6th decimal place (almost always).

I turned in my result in about 5 days, and the company "started implementation," but assigned a "computer geek" to verify my calculations. I think he used Pascal, with keypunched card in/outs, and when he turned in his results about 4 years later the "traces" I managed to get a look at matched mine within <0.1%. The seat was used ONCE (in public knowledge) about 6 years later. The "ejection" actually was "an accident" but at least the guy didn't hit the tail. I was probably the only one who wasn't surprised at that; but I was pleasantly amazed that he took the kick in his ass (potentially as much as 17g eyeballs-down, followed 40 msec later by an eyeballs-in 12 or 14 g) without the spinal damage I apparently was the only one worrying about. G's would have been significantly lower if he was "hefty" but I never got feedback on that.

Around 1985, 40 years after "public ENIAC," there were four engineers among the roughly 60 in my office who had their own "state of the art" calculators. I was using an HP41-CV or -CX (I still have, and use both of them if I don't have Word open to calculate with), and the other three guys had "comparable" TIs. There was a "difference in results" that I was assigned to resolve. Both "calculators" displayed 9 digits after the decimal point, but it took only a quick comparison to the 15-place function tables (produced manually and with mechanical calculators under WPA in the 1930s) to verify that the HP was accurate for all displayed digits, but the TIs' trig functions were "mostly good" to the first 5 with occasional lapses to 4 place accuracy. The rest of what they displayed (and used in calculations) were "random digits."

THAT was "state of the art" 40 years after ENIAC was publicly announced, in most engineering offices. Somewhat more advanced stuff was only accessible by the geeks in the "computer group." (The "Information Technology" bloviation didn't appear for several more years.)

The HP41C "calculators" of that time did essentially everything the co-existing (overlapping?) early DOS computers could do, without "expert" programming, with some limitation on program length and a bit of I/O inconvenience. (You had to copy the results from the display manually.) The "comparable" TI machine had mostly the same functions, subject to the "minor" accuracy problem.

A consistent characteristic of "those good old days" was that every new step produced more useful - and needed - capabilities.

The automotive industry hit the "fuzzy dice and go-fast stripes" phase of "product development" about 70 years ago, and the computer industry appears, to me, to be entering - or well into - a similar era. The "media" business, video and sound, may be a little ahead of the baseline for computers. I sincerely hope the current state of the auto industry doesn't foretell the entire future of publicly available "computers."

John