Crate 410 triode

[adv]

Hello,This is first time to post!I bought a used crate 410 triode.Im having probelms with it though.The amp has a hiss in it which amplifies when I turn the volume knob up,and the hiss amplifies on every knob I turn,(The hiss sounds like a pink nose mic on which is used on a Rain E.Q.) The amp has two pre-amp tubes(ax-7 s ).I pulled the tube fatherest away from the input and the hiss became very faint,and then I pulled the tube closest to the input and the amp went dead,not even a light came on the front of the amp.I would like to repair it myself and Im a newbie in electronics.I need to know,since this is solid state with pre amp tubes,How do I dis-charge(De-Zapp) the amp? I would appreciate If an experience person could give me some pointers on repairing the amp.I would be very grateful for the input. Thanks  ADV

[nashvillebill]

First, you probably blew the fuse inside the amp.  Usually easily replaceable, there may even be a fuseholder on the back of the amp  (otherwise you have to take the amp apart a little bit).  You MUST replace the fuse with one rated exactly the same!!  If it calls for a 5 amp fuse (I have no idea what it takes)  put in a 5 amp fuse, if it calls for 10 put in a 10 amp fuse....

Second--you pulled tubes out while the amp was on???  Not a good idea.  That's what probably blew the fuse.  You can't diagnose "hiss" by randomly removing amp components....

Does it hiss without anything plugged in (without any cords, effects, whatever).
 
Do you have the master volume cranked all the way up?  If so, turn the master volume down and turn the gain up on the preamp.

If you're a noobie to electronics, unfortunately I can't offer too much more advice. 

[teemuk]

You make the amp safe by locating the capacitors that hold a high voltage or energy charge and by discharging these capacitors. These are typically big can-shaped electrolytic capacitors. There will be a "bank" of them somewhere near the power supply and somewhere near the power supply of the tube circuitry. You will surely notice them. Shorting the capacitor terminals together discharges them (with a loud bang) but basically it's a lot more safer to slowly "bleed" the charge by connecting the terminals together through a suitable amount of resistance. The higher the resistance the slower the bleeding will take but the less the resistor will dissipate power. Few kilo-ohms might be a good starting value. Most amps already have some kind of "bleeder" resistor that discharges the capacitors when the amp is powered off but don't count on that in every case. You should always measure the voltage from the capacitor terminals to make sure the capacitor has become discharged. I think this is one of the topics that's been discussed to death already throughout several years. Do a Google search and I'm sure you'll find tons of info.

If you're lucky, fixing this thing is just a matter of a fuse swap but if the replacement fuse blows as well something has failed and you need to start troubleshooting. (Don't try a thrid replacement fuse, it won't cure the problem). Hopefully this is not the case. But if not... Without seeing the circuit I have no idea what pulling the tube off might have damaged. As for hiss in general, that could be a "feature". If the replacement fuse blows and you need to start fixing that thing: Contact LOUD Technologies and ask if they can send you the schematic. The Crate website should have contact information you need. For a newb it's damn near impossible to fix something like this without a schematic. It's arduous even for an experienced tech unless the fault is something extremely obvious. These circuits are quite complex. Should be needless to say but you also must be able to troubleshoot components and work with PC boards without damaging them. Are you? If you have doubts concerning the answer of that question do yourself a favour and take the amp to service. (Naturally, before you do anything else with the amp, try that replacement fuse).

[Jack1962]

1. if it is hissing at this moment, the fuse isn't blown (can't have sound without voltage)
2. never pull tubes on a powered up amp
3. every amp has a small hiss , this is called the amps breath or the amp is breathing.
4. check it with something pulled in .
5. post more info on how you have the amp setup, where you have the knobs turned to,    etc. 

                                          Rock On

[adv]

Hello, Thanks for the response,Nashville Bill,Teemuk, and Jack1962.The amp has a loud hiss with the speakers hooked up,with amp on.Then I unhooked the speakers and there is a slight faint hiss.Yes, I turned off the amp when I did each test,Tube,speakers and etc...I found a site from Keen@eden.com(de-bugging a amp).I followed his instruction format.I already have a schematic from Loud Tech.I did a visual on the P.C. Board for buldging caps.bad resistors,and etc.I dont see anything on a visual base on any defects.The fuse in the amp is good! I bought this amp for the educational purpose of repairing it and when I play (low rent gigs) I want to use it for the purpose of stage drunks and or people looking for a easy rip off of equipment! I have tube amps also that Im partial to.I like too cover my bases also.Ha! I wasnt clear on dis-charging a solid state,That it is done the same way as a tube amp! Yes,It doesnt matter if I turn either the gain,master volume,or go from clean to dirty channel,The amp hisses ,no matter which knob I turn( the hiss noise gets louder).I have looked into a lot of eduacation forums,you tube tutorials and etc! on electronics.Im looking into future eduacation on a degree level.I really appreciate the input from you people.Im trying to limit and narrow down the defects of the amp.I dont have a oscilloscope,but iI do have a digital multimeter.Once again Thanks  ADV

[teemuk]

Sorry, I don't quite follow... At what state is the amp now: Functioning but hissing or "dead" (no sound, indicator light off etc.?) If the latter, let's worry about that first... So, fuse is intact, but what do the power supply voltages read? Are they within the range you should expect them to be, completely gone or something else? Is the mains transformer emitting fairly audible noise? (Ignore all that stuff if the amp is working but just hissing). Also, if the amp shows symptoms of being "dead" you might wish to hook it to a current limiter to prevent further damages in case something has gone short circuit. Even during all servicing this is a good idea. A light bulb in mains line (in series with the amp) will do fine.

Yep, dealing with capacitors in SS amps is the same thing as in tube amps. They are capacitors so nothing changes. Usually the voltages naturally are not as deadly but bear in mind that the current charge in those big caps is often high enough to weld metal etc. So, basically you still need to be cautious. On top of that, I've even seen few old SS amps that run at rail voltages of 120V and up, directly powered from mains, so automatically trusting that SS = low voltage = safe, is not wise. I think it's best to learn to be cautious with everything. Also – and this is very important - solid-state circuits are quite intolerant against over voltage, reverse biasing or high current spikes, so accidentally shorting one of those big power supply caps to a wrong place can even destroy something. The bad thing is that in most cases the damage from something like this is not visible.

Which reminds me. If a solid-state junction deteriorates then, prior to complete failure, it often becomes noisy and hissy. A common cause for deterioration is static electricity spiking that bombards the input stages. The OpAmp in it (I assume there is one) may have gone bad. Those stages usually have a "diode limiter" protection in the input (anti-parallel diodes from signal path to both positive and negative supply rails or back-to-back zener diodes to common or something like that). If it doesn't I'd be even more inclined to assume the input could be the culprit of excess hiss. Changing the input OpAmp might reduce the hiss, especially if you substitute it with a low-noise device. Other sources for hiss are of course high-impedance circuits so keep an eye at them.

Can you post the schematic?

[adv]

crate:
loudtechnologies.com
25001h4_.pdf (511.6 KB)

Hello teemuk,I dont know If I can post this schematic or down load it to this forum.The information (above) is Adobe Reader.I obtained the schematic through loud technologies.Its a crate,GTX410 triode .Yes the amp is functional,I can play it but it makes one heck of a hissing noise.Im just a guitar player,but Im leaning toward the opamp also or at least that has crossed my thoughts.I havent done a volt test on the transformer and power supply yet!I will do that!I was working on my Boss me 50 and traced it down to a cracked board in between the inputs (mono and stereo)female inlets.Someone stepped on the 1/4 jacks.Its (trash).I had to pull off the crate to give that some attention.Hey, I really appreciate your efforts,You know what your talking about.When I first bought this amp,It had a hiss in it when I played it.As time has gone by,The hiss is more prominent.Im not a tech but willing to learn.Im going to read over your last post again and take it to heart.If you can get a chance to look up the schematic I would be grateful ! Thanks alot for your help.  ADV

[J M Fahey]

Dear ADV: trying to open "WWW.loudtechnologies.com/25001h4_.pdf" gets me nowhere.
Googling "25001h4_.pdf " neither.
Would you be so kind as to post the full working link here?
Thanks a lot.
JM

[Jack1962]

Try replacng the 2 12AX7A tubes.

                                                Rock On     

[adv]

 25001h4_.pdf (511.6 KB), 25001p41_...pdf (205.1 KB), 25001p42_...pdf (58.3 KB), 25001p4_.pdf (114.4 KB), 00-277-01...pdf (156.6 KB), 00-277-01...pdf (64.1 KB), 16-13301w...pdf (705.2 KB), 00-277-01...pdf (190.9 KB)  Hello, J M Fahey, I pasted this info from what I got from loud tech. I hope that this is sufficient info.When the representative sent this to my e-mail I opened this through adobe reader.Thanks for your efforts! Jack I replaced the pre-amp tubes.The owner manual I had originally said to do that.It didnt change much! Thanks to everyone for your input! ADV

[Jack1962]

bro all I can tell ya is email me the diagram at Jackylatham1962@wmconnect.com and I will look at it at then we can go thru it.

                                                    Rock On