| Author |
Topic: So you buy a $2500 amp |
Jim Sliff
From:
Lawndale California, USA
|
Posted 24 Feb 2018 7:37 pm |
|
| Quote: |
Hey Jim, just for my own learning and awareness, what are some of the maintenance tips you would suggest for tube amps?
"Normal" maintenance:
1. Electrolytic filter capacitors have a service life of roughly 15 years. While they can last longer (and die much earlier if an amp is stored unused for an extended period) A "cap job - which consists os ONLY replacing those and, in fixed bias amps the "bias cap" is recommended at 12-15 year intervals. And in cathode bias amps the power tube cathode cap should be replaced.
Many techs will ONLY do this if you ask them - so ask. And if a tech tells you 30 or 40 or 50 year old filter caps are just fine or "tested OK" - find a new tech!
And ANY time filter caps - or parts in the driver - are replaced the bias must be checked - and usually adjusted. See below...
2. At that time it's most cost-effective to have other work done:
Check bypass electrolytics and coupling caps for electronic (not physical - which would be obvious) leakage and replace as necessary
Check all voltages in accordance with the schematic (or in Fender's case, some voltages are only shown on the layouts). With vintage - tweed, brown, BF and SF amps - voltages will be higher than shown as "spec" numbers were based on lower wall voltages. That's OK.
If there's more "hiss" than seems normal I suggest replacing the preamp plate resistors at this time as well. May or may not reduce the hiss but they usually start to "go" at some point.
Many (I'm one of 'em) suggest installation of 3 watt or higher screen resistors if they're not already there to protect the amp.
On amps over 25 years old I generally replace the (often 1.5k) grid resistors on the power tube sockets with metal film if they're carbon comps. They are subject to quite a bit of heat. Another "amp health" item.
clean and lube all pots and jacks and tighten all of them. DO NOT USE contact cleaner! Only "cleaner/lubricant". Use WD40 or similar crap and I shall hunt you down for a Wiffle bat thrashing. 
Clean, lube and retension all tube sockets. this one gets skipped WAY too often.
"tap test" preamp tubes for noise. And if newer type European tubes or Chinese tubes are installed replaced all of them. NOS tubes from the 50's 60's and 70's can last for many decades - something unlikely with newer ones.
Check the power tube plate voltage and the bias. For fixed bias amps set the bias at roughly 70% dissipation (the plate voltage HAS to be measured to calculate tis) - but then play normally and make small adjustments for tone if necessary. Once it's "dialed in" recheck to ensure it's in a "safe" zone . This last one takes a tech that will work with you, not one that just arbitrarily chooses settings. And setting bias based only on math is a bit odd, since "math" has no tone.
Some amps have no bias pot,but changes are made by simple resistor changes (usually hooking up a decade box to try different values is the best approach). But buying tubes with the "same gain/value/number/voodoo mark" as the old tubes DOES NOT mean you don't need to check the bias, as old tubes drift and new tubes - even marked the same - aren't always identical. Or even close. No matter what Mesa Engineering says (snicker).
Even cathode bias amps have a bias setting that needs to be checked. "Self bias" is a misleading term.
And Groove Tubes are mostly the same tubes everyone else sells, and there's nothing magic about their testing.
I also check all transformer bolts, tube socket mounts, baffleboard screws, speaker mounts - and make sure speaker leads are FIRMLY attached, especially in one-speaker amps. A disconnected speaker can cause a fried output transformer.
This seems like a HUGE, expensive list - but it's not. Most items take just a few minutes. I tell "vintage shoppers" who have no tube amp experience to budget $150-350 on top of amp cost for normal service - which nearly every used vintage amp needs. The bottom number generally covers a cap job and checkup/maintenance on most Fenders; the upper number generally includes power tubes with the driver tube, always replaced at the same time). But "repairs" and preamp tubes can kick things into the %400 range pretty quickly.
ONCE basic service is done properly maintenance becomes easy - cap job every 15 years or so, checkup and pot/jack/socket stuff, and periodic tube replacements.
I find that well-maintained vintage amps rarely need repairs. |
_________________
No chops, but great tone
1930's/40's Rickenbacher/Rickenbacker 6&8 string lap steels
1921 Weissenborn Style 2; Hilo&Schireson hollownecks
Appalachian, Regal & Dobro squarenecks
1959 Fender 400 9+2 B6;1960's Fender 800 3+3+2; 1948 Fender Dual-8 Professional |
|
|
|
Jim Sliff
From:
Lawndale California, USA
|
Posted 24 Feb 2018 7:47 pm
|
|
The standby switch prevents the tubes from being hit with plate and grid voltages.
If it makes you feel good, turn on the power switch, wait a bit (30 seconds, or a minute, or an hour) and then turn on the standby switch.
When turning the amp off turn both switches off at the same time. The standby switch serves no "shutdown" purpose.
And - although there are endless debates about the subject - standby switches are not found on many high-end tube amps, most audiophile equipment, and an increasing number of amp techs will tell you they are totally unnecessary.
Most amp techs don't use them - ever.
And using things like "light bulb limiters" or a Variax to slowly bring new filter caps up to voltage are silly. NO manufacturer uses such doodads - I don';t know any good amp techs who do either (they may use a Variax fr specific voltage *testing* - but that's it)
Manufacturers have built and always will build amps and them turn the things on. I've never heard of a new. good quality electrolytic filter cap blowing up unless there's a problem in the amp that should have been found through testing LONG before it was "turned on".
_________________
No chops, but great tone
1930's/40's Rickenbacher/Rickenbacker 6&8 string lap steels
1921 Weissenborn Style 2; Hilo&Schireson hollownecks
Appalachian, Regal & Dobro squarenecks
1959 Fender 400 9+2 B6;1960's Fender 800 3+3+2; 1948 Fender Dual-8 Professional |
|
|
|
Erv Niehaus
From:
Litchfield, MN, USA
|
Posted 25 Feb 2018 6:48 am
|
|
Thanks, Ken! 
Erv |
|
|
|
Donny Hinson
From:
Glen Burnie, Md. U.S.A.
|
Posted 25 Feb 2018 7:37 am
|
|
| I think most of the reasoning behind the standby switch was to kill the sound, but keep the filaments "hot". Instantaneous failures of tubes (as opposed to them slowly just wearing out) were only due to three causes - envelope (glass) breakage, open filaments, and inter-electrode shorts. Aside from encasing the tubes in metal, hiding the tubes inside the amplifier enclosure or encasing them in a cage was about all they could do to reduce breakage. Filaments nearly always opened up when the amp was turned on, so reducing the number of on/off (thermal shock) cycles definitely helped that issue. I think this came from the old "Once it's running, keep it running" ethic that probably started with engines. Inter-electrode shorts were nearly always caused by vibration induced by physical handling, and to a lesser degree by the innate vibration of the tube from speaker forces. Manufacturers could only reduce that by using a shield or other retainer, coupling it firmly to the (more solid) chassis, or by separating the amp and tubes from the speaker enclosure. |
|
|
|
Steve Sycamore
From:
Sweden
|
Posted 26 Feb 2018 12:47 am
|
|
| Yes, the standby circuit engages a heater circuit. It's quite important to warm the tubes before power starts flowing through them. A sudden application of strong current could cause a very sharp temperature change or wild deflection of the electron trajectory which could crack, burn or warp metal and glass and result in catastrophic failure. Remember, you're pumping billions of electrons through those tiny channels. |
|
|
|
Mike Scaggs
From:
Nashville, TN
|
Posted 26 Feb 2018 4:26 am
|
|
If anyone cares to educate them selves on standby switches read this.
http://www.valvewizard.co.uk/standby.html
This is solid technical information
_________________
I can explain it to you but I can't understand it for you
Zum double Hybrid 8x9, 64 Twin (JBLs), p2pAmps Bad-Dawg, p2pAmps Tremendous Reverb, Visit my website www.p2pamps.com |
|
|
|
Ken Byng
From:
Southampton, England
|
Posted 26 Feb 2018 6:04 am
|
|
Thanks Mike. That info is the antithesis of most instruction on the use of the standby switch that I have ever read, including that from Fender with their new tube amps. However, what the 'Valve Wizard' says does make some sense. I assume that the author is British as we refer the the units as valves as opposed to our cousins in the USA who call them tubes.
_________________
Show Pro D10 - amber (8+6), MSA D10 Legend XL Signature - redburst (9+6), Sho-Bud Pro 111 Custom (8+6), Emmons black Push-Pull D10 (8+5), Zum D10 (8x8), Hudson pedal resonator. Telonics TCA-500, Webb 614-E, |
|
|
|
Donny Hinson
From:
Glen Burnie, Md. U.S.A.
|
Posted 26 Feb 2018 8:46 am
|
|
That article is good...as far as it goes. However, it's more just an argument against traditional standby switches than it is useful information on tube failure. Since it does not address deterioration due to repeated on/off cycles, it completely ignores one of the main causes of tube failure.
Frankly, I don't care how you accomplish it - with a standby switch, or just leaving the amp on and turning down the volume. Or easier than that, just unplugging the guitar cord from the amp. One on/off cycle a night for filaments is better than five. |
|
|
|
Mike Brown
From:
Meridian, Mississippi USA
|
|
|
|
Steve Sycamore
From:
Sweden
|
Posted 27 Feb 2018 2:15 am
|
|
Informative articles Mike and Mike, thanks! Maybe the main issues against the "perfect" solutions that the 2 authors suggest about rectifiers are that:
1) The rectifier tubes that give the authentic sag and magical bounce are the older models like the 5U4. Those are used currently in many of the most capable Mesa amps and enthusiasts do not want to be without them.
2) Using either diodes or neon tubes goes pretty far against the wishes and tastes of both vintage enthusiast players and most designers and technicians I believe.
Regardless, I'm now convinced that leaving the amp in standby mode after it has warmed up is not a great idea. |
|
|
|
Tony Glassman
From:
The Great Northwest
|
Posted 27 Feb 2018 6:55 am
|
|
| Quite a " topic drift" from the OP ! |
|
|
|
Josh Yenne
From:
Sonoma California
|
Posted 10 Mar 2018 7:30 pm
|
|
Generally I try to get almost nothing through the monitor...for my instrument... and actually overall... as the steel player we are often far "stage... right or left" I put my amp as far out as possible to get a straight shot to my ear... putting it though the monitor is by definition "bi-amping" it... although I know they say it is "flat" I really try to take as little from the monitor as possible... thats just me.
Generally sound guys like this.. but then again I dont play with massively loud bands usually. If I have to get some "fill" from the monitor I try to take as little as possible so it is just filling from the front.
I also play tube amps and like them a bit hairy and pushed so i like them cranked a bit... just my preference.
I have had MANY a sound guy thank me for taking as LITTLE as possible through the wedge as I absolutely need... when everyone starts cranking the monitors it turns into an absolute disaster up there. |
|
|
|
Jim Sliff
From:
Lawndale California, USA
|
Posted 11 Mar 2018 1:12 pm
|
|
| Quote: |
| It's quite important to warm the tubes before power starts flowing through them. A sudden application of strong current could cause a very sharp temperature change or wild deflection of the electron trajectory which could crack, burn or warp metal and glass and result in catastrophic failure. |
That happens SO rarely it's simply a non-issue. In 50+ years of working on tube equipment I've never had an "instantaneous power-related tube failure". Nor heard of any unless there was some other issue in the amp that spiked voltage beyond "spec".
Even in in amps like Deluxe Reverbs that run 6V6's beyond spec voltage it only occurs with low-quality tubes. That's not a "standby switch" issue.
The majority of other amp techs I know don't use standby switches and they are not standard equipment on many amps because they're not necessary. They are somewhat "traditional" so some still install them.
_________________
No chops, but great tone
1930's/40's Rickenbacher/Rickenbacker 6&8 string lap steels
1921 Weissenborn Style 2; Hilo&Schireson hollownecks
Appalachian, Regal & Dobro squarenecks
1959 Fender 400 9+2 B6;1960's Fender 800 3+3+2; 1948 Fender Dual-8 Professional |
|
|
|
Steve Sycamore
From:
Sweden
|
Posted 13 Mar 2018 2:16 am
|
|
| Quote: |
| In 50+ years of working on tube equipment I've never had an "instantaneous power-related tube failure". Nor heard of any unless there was some other issue in the amp that spiked voltage beyond "spec". |
I was fortunate that an EL34 blew and took out only the fuse about a second after switching from standby to full power. Maybe that was triggered by voltage spikes on my power grid? I live at the terminal of an extended line which tends to be flaky with dimming lights during high current loads. Time to look into power conditioning? |
|
|
|
Erv Niehaus
From:
Litchfield, MN, USA
|
Posted 13 Mar 2018 7:13 am
|
|
| I've got a power conditioner in my rack that measures the current when I turn on the power. It corrects the voltage if it isn't too out of line and if it is, it shuts the power off. |
|
|
|
Jim Sliff
From:
Lawndale California, USA
|
Posted 13 Mar 2018 9:54 am
|
|
| Quote: |
| I was fortunate that an EL34 blew and took out only the fuse about a second after switching from standby to full power. Maybe that was triggered by voltage spikes on my power grid? I live at the terminal of an extended line which tends to be flaky with dimming lights during high current loads. Time to look into power conditioning? |
In a case like that I'd use a voltage regulator/conditioner. I used to play a lot of outdoor festivals that "acquired" power from all kinds of sources including generators. I used a regulator/conditioner that kept power at a clear 117VAC.
The EL34 that blew when hit with operating power would have likely done the same thing if the filaments had been cold. What happened was a typical tube failure unrelated to whether filaments were pre-heated (and the tubes were warm) or not.
Just as a curiosity - what brand/model of tube blew?
Power-related sidebar - *never* allowed a stage hand or sound "engineer" to touch a power cord or ground switch/ground lift without your knowledge and approval.
They (or you) can easily create an electrocution source. Every player should understand grounds and electrical safety. Most players don't know (or check) whether power outlets at home or at gigs are grounded and have correct polarity.
_________________
No chops, but great tone
1930's/40's Rickenbacher/Rickenbacker 6&8 string lap steels
1921 Weissenborn Style 2; Hilo&Schireson hollownecks
Appalachian, Regal & Dobro squarenecks
1959 Fender 400 9+2 B6;1960's Fender 800 3+3+2; 1948 Fender Dual-8 Professional |
|
|
|
Ian Rae
From:
Redditch, England
|
Posted 13 Mar 2018 2:39 pm
|
|
| On 27 Feb Tony Glassman wrote: |
| Quite a " topic drift" from the OP ! |
... which was "So you buy a $2500 amp..."
So I did, because I thought it would make it easier to hear myself when things get loud. At first it made it harder! Then I realised that I'd been listening to the distortion from the old amplifier. It took me a while to re-educate my ears to detect the clean sound, and it's fine now. My regular gig is an open-mic in a small room with just vocals and maybe acoustic guitar on the PA, and it varies from folk singers to punk bands, and my Telonics rig sounds better for the quiet stuff (because it's so quiet electrically) and better for the loud stuff (because it's so loud). Win-win, no compromise.
_________________
Make sleeping dogs tell the truth!
Homebuilt keyless U12 7x5, Excel keyless U12 8x8, Williams keyless U12 7x8, Telonics rack and 15" cabs |
|
|
|
Steve Sycamore
From:
Sweden
|
Posted 14 Mar 2018 8:08 am
|
|
| Jim Sliff wrote: |
| Just as a curiosity - what brand/model of tube blew?. |
It was a 60's or 70's Mullard in apparent great shape. I got about 40 hours playing time before it blew. Sounded superb. |
|
|
|
Jim Sliff
From:
Lawndale California, USA
|
Posted 15 Mar 2018 12:30 pm
|
|
| Quote: |
| It was a 60's or 70's Mullard in apparent great shape. |
"Apparent great shape" sounds to me like it was a used tube and you got 40 hours or so of use out of it. Am I wrong in guessing that?
If it was a NOS Mullard I'd be surprised but still wouldn't blame the amp/switches/power. If it was a used tube I'm sorry to tell you this - bu there is no such thing as "apparent great shape". Nice physical appearance of a tube means nothing as far as performance or life.
_________________
No chops, but great tone
1930's/40's Rickenbacher/Rickenbacker 6&8 string lap steels
1921 Weissenborn Style 2; Hilo&Schireson hollownecks
Appalachian, Regal & Dobro squarenecks
1959 Fender 400 9+2 B6;1960's Fender 800 3+3+2; 1948 Fender Dual-8 Professional |
|
|
|
Steve Sycamore
From:
Sweden
|
Posted 16 Mar 2018 1:02 am
|
|
| The electrical measurements on the tube were excellent as obviously the tone was also. I don't know if anyone sells actual NOS Mullards anymore unfortunately, at least not at a semi-affordable price. So if you want a good condition example you have to take a chance. Fortunately it's a lot easier to find great 6L6's than EL34's. |
|
|
|
Jim Sliff
From:
Lawndale California, USA
|
Posted 17 Mar 2018 5:21 pm
|
|
| Quote: |
| The electrical measurements on the tube were excellent |
OK, I'll guess again.
You bought tubes on eBay from a seller that tested them with a) a Hickok tester of some sort or 2) a Military TV-7U.
What do I win?
eBay tube sellers, for the most part, are used to dealing with the hi-fi world - and voltage requirements are MUCH different. But those who use gear like I ]noted and say they're selling guitar amp tubes either don't know what they're doing or don't care.
That type of testing is useless for guitar amp purposes. 99.9% of the tube testers used by eBay sellers hit the plates with 187 VDC maximum.
But guitar amps generally hit EL34's with 350-500VDC. 6L6's get 300-460-ish; 6V6's 300-420.
187 volts is simply NOT enough to stress the tubes for guitar amp use, and test results at that kind of voltage are irrelevant - they will change at higher voltage (despite some claims to the contrary).
Power tubes can be tested for shorts and basic operation, but for guitar amp use they ALSO need to be tested and the bias checked (even if cathode biased) in a guitar amp. Matching also has to be done in an amp - an amp that is fully serviced with a driver circuit that's either precisely balanced or the "imbalance" is known and matching calculated and tested accordingly.
Used preamp tubes intended for 1) gain stages or 2) driver/phase inverter use in many amps (most, actually) also need higher voltages, although not by a huge amount. Usually. But if you don't know the preamp voltages your amp has it'll be a crapshoot buying those as well.
And NO noise tests are performed by these tube testers.
A FEW sellers own high voltage testers. But if so they say so.
And to make it worse - tube testers have to be calibrated every few years. It's 1) expensive, and 2) not many techs know how to do it properly. If the tester was calibrated over 5 years ago ANY results except shorts testing is pretty much garbage.
This is why NOS tubes cost more than so-called "tested" pulls (used tubes), and high-quality pulls tested at high voltage cost almost as much as NOS tubes.
I have a big tube stash but buy "tested" pull 6V6 pairs once in a while as my stock is a bit low. I discard about 1/3 of them and no pair that is "matched" has ever actually matched - I've had to re-test with my calibrated Hickok 6000 and match in one of the amps I use for the purpose.
Last - if sellers test tubes with an "emission" tester you will know if the tube is "bad" or "functional". But absolutely nothing about quality/performance. Those are great testers to have if you stumble on dozens of tubes so you can weed out the bad ones. But you still have to actually test the performance, perform matching and so on in an amp.
Or in short - you get what you pay for.
_________________
No chops, but great tone
1930's/40's Rickenbacher/Rickenbacker 6&8 string lap steels
1921 Weissenborn Style 2; Hilo&Schireson hollownecks
Appalachian, Regal & Dobro squarenecks
1959 Fender 400 9+2 B6;1960's Fender 800 3+3+2; 1948 Fender Dual-8 Professional |
|
|
|
