crate v 50 switch mode power supply issues

[phsyconoodler]

Anyone ever ditch the switchmode power supply in a Crate V50 and add a power transformer?

 Can't find a schematic for this amp or I would just do it. There seems to be a lot of these amps going down cause of pooched power supplies.
 I have a nice HRD PT sitting here doing nothing right now. The color codes are not consistent with tube amps so it may be a bit difficult to graft in without a schematic.
  I hate throwing stuff away.The amp sounded ok before the power supply burnt up.I wouldn't mind using it for a jam amp.
Anyone that could point me in the right direction would be thanked profusely.

[eleventeen]

Without a schematic = tough go. Even with a schematic, there are all the usual mechanical issues.

I would encourage you, though, to go find a replacement switcher if the idea does not offend. If the p/s is indeed separate and mounted on another board, these power supplies are very, very standardized items at this point. I found this to be the case when I was repairing computer terminals about 15 years ago. I found a suitable replacement and the mfr happened to be discontinuing them, had half a dozen, and sold them to me for $6 each. Very rarely does a manufacturer (of amps or anything else) build their own supplies, particularly small switchers. If you can find a suitable replacement there are probably 11 different manufacturers that make *exactly* the same and I do mean exactly, complete with the same output connector. You might be able to grab one new in the box on fleabay for $10, delivered. That's cheaper than a p/t altho I realize the p/t you are eyeing is just sitting there.
It's still going to be several hours of futzing around with the thing to mechanically mount it, build a little filter rectifier deal, and lash it into the Crate.

Regards...

[phsyconoodler]

Hmmmm....you may be right.I will try and find a replacement first and see how that goes.But there is a reason why these amps are always broken down and that goes directly back to the fact that a switch mode power supply doesn't belong in a tube amp IMHO.

[eleventeen]

Lemons  >  Lemonade. Bet you could research and find out a suitable replacement, buy a dozen of them at a whack for $10 each or less, and sell them as NIB replacements for $40. You got your test bed.

[DummyLoad]

you have to a sadistic AND masochistic idiot savant with bipolar disorder to work on switchmode regulators. rip it out, put in linear PS.

--pete

[PRR]

You are unlikely to find a supply with the same specs except as a Crate-replacement.

3.3V, 5V, 12V are standard boxes. 300V is _not_ a common part in today's low-volt world.

As for a PT: it's a tube amp. How hard can it be?

Well, it would be a lot easier if you had a working one to compare to.

Are the heaters in parallel at 6V? Then ready to go. However in switcher-land it may have been wiser to series them at 12V or more. Can you re-wire the heaters? If they are on PCB you probably "need" to re-wire with twist-pair to use AC heat without hum.

What's the main B+ voltage and current? 50W in two 6L6, kinda has to be 450V at 200+mA. Though the base rig will work at lower voltage and current at lower output.

The screen and small-bottle B voltages surely step-down the usual way, separate from the actual power supply.

[eleventeen]

Sorry, didn't realize or even consider that it was a tube amp!

Then the p/s is definitely nothing generic. Never mind.

[phsyconoodler]

It's probably rather easy except for the channel switching.That's why a schematic would help to figure it out.
 I may just pop in the transformer,wire up the heaters and screens and just use the clean channel anyway.
Even though it's a made in China piece of crap,it did sound ok before it blew.The tubes test good and the speaker is adequate.
  Nothing to lose and a couple hours work to saw a hole for the PT and graft in some heater wiring.

[phsyconoodler]

Bingo! Found some schematics and a PCB layout. Looks straightforward.

The power supply supplies 420V DC,-63v presumably for bias,+ and - 17v for relays and 6.3v for heaters.

The HRD PT has those taps already.May be easier than I thought.

[phsyconoodler]

So I removed the burnt components in the power supply and it was easy to do so,but I was wondering if I should replace them and try it?
 What usually goes in the power supply to make them burn a resistor?In this case it is one burnt resistor that is surrounded by a diode and a .001uf/1kv cap and a couple other 1 watt resistors.All of the legs on the resistors and the diode have ferrite beads on the leads as well.
 Unfamiliar territory for me but it doesn't look too daunting.

[DummyLoad]

would you consider posting the schematic?

--pete

[sluckey]

The VA product exceeded the resistor's power rating.

[PRR]

> What usually goes in the power supply to make them burn a resistor?

A semiconductor.

Which often doesn't leave burn-marks.

[phsyconoodler]

Interesting.There is a single diode with a ferrite bead right in the center of the cluster of resistors.Guess I'll change that too.
 Nothing to lose by trying.


 The ling to the schematics are here : schematics.number26.org

[phsyconoodler]

changed the parts but it doesn't work,so I'm not spending any more time on it.
 The transformer is going in!

[eleventeen]

Fixing switchers is a black art of some kind. I have known people who could do it but I never learned their voodoo methods, other the big blue variac they had on their bench. You DO realize that switchers require a load to work, yes?

[phsyconoodler]

Hm....you mean tubes in and speaker plugged in? I am totally unfamiliar with switchmodes.

[phsyconoodler]

I didn't try and fire it up on the bench as its rather easy to install.It doesn't work.It puts out 65v DC and nothing else,no heaters voltages,nothing.
 The PT will be easy to install and it has the necessary taps to run the relays too.I just need filter caps,a full wave bridge for the PT and the 17v taps and off I go.

[eleventeen]

To fire up almost all switching p/s "on the bench" you have to install some kind of load on the major outputs and possibly *all* the outputs. For the most part these would be resistive loads calculated to convince the p/s that "the rest of the amp" is lashed up to it. If the HV is supposed to be 450 DC volts, for example you'd probably be looking for let's say a 50 ma load so that would be 450 / .05 = a 9K ohm resistor (10K would be fine = 45 mils) @ I*I*R = 20.25 watts actual so 25 watts minimal and it would get pretty warm.

Point being, it's in this sense not all like a PT > 5Y3 > filter caps which will give a strong output even with nothing hooked up acting as a load.

It would not surprise to know that you'd have to do the same with the heater portion: maybe 3+ amps across 6.3 volts = 2 ohms, I*I*R = 9*2 another 20 watter.

Here's where the junkbox of parts torn out of dead TV sets comes in.

Edit: Incidentally, I agree with the consensus that a switcher powering up a tube amp is borderline detestable.

[phsyconoodler]

There must be something else fried in the power supply.It just is a colossal waste of time at this point.
 I have no clue how a little transformer and a bunch of little itty-bitty parts on a PC board can handle the current from a tube amp.Maybe they can't for long and that's why you see so many junky Crate amps in the trash bins.

[PRR]

> have no clue how a little transformer and a bunch of little itty-bitty parts on a PC board can handle the current from a tube amp.

Big fire. To fight it you need 60 Gallons of water a minute.

The pumper-truck broke. You need to improvise a pump. Piston-pump may be easiest.

If you have a 60 gallon barrel and make a piston for it, you must work it once a minute.

If you have a 1 Gallon bucket, you must work it 60 times in a minute.

If you only have a teaspoon, you must pump 1 teaspoon of water 46,154 times a minute to get your 60 gallons a minute.

The switchers do run frequency about 40,000 (but per second). So they can use a "pump container" (transformer) hundreds of times smaller than 60Hz iron.

One thing: in the teaspoon pump, stuff like one-way valves have to work FAST. The same problem with electronic rectifiers. A 1N4007 is not fast enough for a modern switching-supply. (Imagine the pump-valve doesn't shut fast enough. Water back-flows, a waste of energy.)

If you need a steady flow: the 60-gallon barrel pumps a big slug of water infrequently. The teaspoon pump has tiny gushes frequently. A storage/smoothing system can be smaller.

They do work. All your digital toys use switchers. A good desktop PC uses more Watts than your average tube amp. PC power supplies fail, but not all THAT often.

> It just is a colossal waste of time at this point.

Agree. It's specialized stuff, outside what you want to do and are good at.

The dumb old 60Hz PT and parts _is_ an acceptable replacement (probably; depends on fit and what wacky things they did with a switcher's flexibility).

[phsyconoodler]

Agree. It's specialized stuff, outside what you want to do and are good at.

The dumb old 60Hz PT and parts _is_ an acceptable replacement (probably; depends on fit and what wacky things they did with a switcher's flexibility).

Indeed. I'm good at fixing cars and was a pro at the lost art of rebuilding carburetors.That and Volkswagen air cooled engines.
  A switchmode power supply is very modern to me and your description makes sense.I did put in a 3 watt FR diode in place of the 2 watt FR207 that was in there.The power supply on my computer did pack it in last week by the way,but I guess a 10 year old PS is considered way beyond it's lifespan.

[mgalicki]

So fellas, I have the same deal with a Crate V33. It blew something in I beleive the power supply when I adjusted a faulty variac. SO no way to fix this ting?? There has to be somebody out there that knows how??
Or any ideas about using the rest of the amp to build something else??
Thanks for any input,
Mark

[PRR]

The crap switch-power in some Crates is not a new problem.
http://www.thefret.net/showthread.php/15880-Crate-V-series-and-Class-D-amplifiers-in-guitar-bass-amps
https://www.thegearpage.net/board/index.php?threads/help-with-crate-v33-212-amp.1155410/

The amplifier schematic is available, but not the power unit.
https://www.thetubestore.com/crate-schematics

It is functionally same-as a "36Watt", a standard clone. So you "could" replace the power pack with a conventional transformer(s). The V33 adds DC heat on some tubes and +/-14V power for opamps and relays, and I don't think everything is annotated on the amplifier schematic.

[Latole]

Power supply and more here; see answer no 2. ;

https://music-electronics-forum.com/forum/amplification/guitar-amps/theory-design/40081-crate-v50-power-amp-schematic-please

[mgalicki]

I have attached the SMPS schematic for my V33! Please let me know if there's hope.

[mgalicki]

I have attached the SMPS schematic for my V33! Please let me know if there's hope.

Here are the burnt items on the board.
Thanks for any assistance you can me to get it back in working order.

[Redwood]

I have *exactly* the same failure in a V18, a smaller 1x12 running just a pair of EL84 tubes but using exactly the same SMPS, even the same REV and date on the board.
Did you ever get yours going?  I'd love to know which components you replaced before determining it couldn't be fixed and whether you took any voltage measurements around the board to see if you could trace the defect.  Before I found this thread I was just going to replace those three resistors, the diode, the red cap, and the pair of electrolytic cans in that area.  But if you did all that and got nowhere I guess I might just abandon the project.  This amp has been sitting in my room for at least 5 years since it failed on me and I've got so many others I'm just now getting around to it. 

The idea of replacing the SMPS with a PT is interesting but honestly if I were going to attempt all that I think I'd be more inclined to just strip the entire chassis and start from scratch with a Princeton circuit or something like that.

I have attached the SMPS schematic for my V33! Please let me know if there's hope.

Here are the burnt items on the board.
Thanks for any assistance you can me to get it back in working order.

[megatrav]

Sorry for resurrecting an older thread but my nephew just brought me his amp and the power supply went out.

Were you successful in replacing it with a pt?

[WimWalther]

Tube gear with SMPS..

"But, it sounded like a good idea at first."