Retubing a Crate Palamino V8

[Duff]

I'm almost positive I need to retube my Crate V8, five watt, amp. It hums fairly loudly and crackles sometimes. It does not hum, however when you pull out the guitar plug from the input, it is silent.

I bought a new Monster Cable and it hums loudly with that too. When I smack on the side or top of the amp the hum either changes pitch, reduces in volume, increases, or goes away.

I can easily remove the chasis, as I am mechanically inclined and have tools, so this is not a problem.

Do I need to bias the Crate Palamino V8? I can't find my digital tester but would buy a new one if I could bias the amp myself.

So, does the amp require biasing, and, can I do it myself?

Any advice, shared expertise from someone with a V8, or other ideas will be greatly appreciated.

Right now that is my favorite amp, using a Digitech RP350 into it to get tones the amp would not normally be able to produce with its three knobs only. Great amp though.

Thanks in advance,

Duffy

[M29]

Hello Duff,

It sounds to me like you might have a bad connection on the input jack. Especially if you tried different cords and can tap on the chassis and get a reaction. If you can, try re-flowing the solder connections on the input jack. It can't hurt unless you get a cold joint in your soldering:D

No idea on the biasing, I am not familiar with that amp.

M29

[tunghaichuan]

Duff,

The Crate Palomino V8 is a cathode bias amp. Most of the time with cathode bias amps, you can just plug and play. Try replacing the tubes with known good ones.

Unless you know what you're doing, I'd caution you not to remove the chassis. There are lethal voltages in tube amps. If swapping out the tubes doesn't fix the problem, I'd encourage you to take it to a competent tech for servicing.

Seriously, if you don't know how to work on high voltage vacuum tube equipment safely, you are literally taking your life in your hands.

tung




I'm almost positive I need to retube my Crate V8, five watt, amp. It hums fairly loudly and crackles sometimes. It does not hum, however when you pull out the guitar plug from the input, it is silent.

I bought a new Monster Cable and it hums loudly with that too. When I smack on the side or top of the amp the hum either changes pitch, reduces in volume, increases, or goes away.

I can easily remove the chasis, as I am mechanically inclined and have tools, so this is not a problem.

Do I need to bias the Crate Palamino V8? I can't find my digital tester but would buy a new one if I could bias the amp myself.

So, does the amp require biasing, and, can I do it myself?

Any advice, shared expertise from someone with a V8, or other ideas will be greatly appreciated.

Right now that is my favorite amp, using a Digitech RP350 into it to get tones the amp would not normally be able to produce with its three knobs only. Great amp though.

Thanks in advance,

Duffy

[Duff]

I did not take that apart. I can probably do that but might have to remove the chasis.

Tung: what is the problem in removing the chasis? Any specific concern areas?

I'm thinking I can find info on the internet like on Eurotubes page that give you instructions on how to safely handle tube amp work.

Is anyone aware of any directions regarding protecting yourself from the lethal voltages present in tube amps?

Help is definitely appreciated.

People must do this all the time, and do it safely. Tube amps have to be re tubed frequently. I lot of people must like to do it themselves, safely, of course.

Thanks for the concern Tung. I will not attempt the job unless I am sure that I can do it safely. Have you done it?

Duffy

Some pictures of guitars:

[tunghaichuan]

I did not take that apart. I can probably do that but might have to remove the chasis.

Tung: what is the problem in removing the chasis? Any specific concern areas?

I'm thinking I can find info on the internet like on Eurotubes page that give you instructions on how to safely handle tube amp work.

Is anyone aware of any directions regarding protecting yourself from the lethal voltages present in tube amps?

Help is definitely appreciated.

People must do this all the time, and do it safely. Tube amps have to be re tubed frequently. I lot of people must like to do it themselves, safely, of course.

Thanks for the concern Tung. I will not attempt the job unless I am sure that I can do it safely. Have you done it?

Duffy

I've been building and working on tube amps for over 10 years now. I've lost count how many times I've biased cathode bias amps. I've gotten shocked a few times, mainly due to carelessness, but I'm still here mainly due to following some safety guidelines.

Here are a few sources:

http://www.drifteramps.com/safety.html

http://www.ampmaker.com/index.asp

http://aikenamps.com/SafetyTips.html

If you Google "tube amp safety" you'll get a few more.

Generally you only want to work on tube amps when they are unplugged, off and have had the power drained from them. With biasing, the amp has to be turned on. Working on a live chassis is inherently dangerous.

When probing a live chassis, you never want to put both hands in the chassis at the same time. Put one hand in your pocket to keep from using it. That way if you get shocked, the current won't travel across your heart and stop it.

With the amp off and unplugged, the main area of concern is the power supply filter caps. These can store a charge long after the amp has been turned off. To safely work on an amp with the amp turned off and unplugged, you will need to drain the filter caps. Don't short them with a screwdriver, you can damage the caps and/or the amp this way. You can make a device to drain the caps with two pieces of 18-22ga. 600v wire, two insulated aligator clips and a 1k ohm 5W resistor. Basically you solder the two pieces of wire to the resistor and then solder an aligator clip to each end of the wire. Clip one end of the device and then clip the other end to the positive terminal of the first power supply filter cap. NOTE: this is only to be used with the amp off and unplugged. Leave the device in place for a few minutes and use your DMM to check to see if there is any residual voltage. I usually leave the device in place while working on the circuit and take it off right before I power the amp up.

With the amp on you have to worry about the 120v AC from the wall. I've gotten bit several times.

Here are some instructions for biasing a Valve Junior which has a similar output section to the V8:

http://www.diycustomamps.com/valvejunior.htm#vjbias

In your case, the part number of the cathode bias resistor is R17.

One thing: the schematic shows 100 ohms for R17. If your power supply voltages are anywhere near 300v (the schematic doesn't say), R17 is too low. Generally I like to use a 270 ohm resistor to get the EL84 biased so that it is not over its dissipation.

However, one of the reasons you may like the sound of the stock circuit is that it is overdissipating the EL84. If you rebias so that the EL84 is within its dissipation rating, the tone may change and you may or may not like it.

One other thing that occured to me is that with PCB-based amps like the Crate, is that sometimes there are cold solder joints on the PCB. Also amps like that tend to use ribbon connectors which can come loose and cause intermittent problems like you described.

My recommendation is to swap out the EL84 and 12AX7 tubes and see if that clears up the problem before opening up the chassis and exposing yourself to hight voltage.

Please post questions if anything is unclear.

BTW, one excellent source of info on single ended amps is the sewatt.com (http://www.sewatt.com/)forum. You have to join to post, but it is set up to help newbies learn to work on amps safely.

HTH,

tung

[F_BSurfer]

The V8 only has two tubes a preamp 12AX7 and a power tube EL84 and it is cathode bias the preamp tube can be replaced without any problems but the power tube you might have to remove the chassis from the cab
Friend has this amp and have experimented with it quite a bit JJ's el84 is a good cheap replacement the preamp Tung Sol new production is a good replacement for a little more crunch JJ's high gain

Tung gave some excellent links great places to learn how to work on your amp!!!!!!!!

tubes I like http://www.tubedepot.com/index.html single tubes you have to call

[Duff]

Surfer

I am wondering how you would get out and put in the preamp tube on the V8 without taking out the chasis. I could barely touch it when I was trying to locate it.

How would you line it up to make sure you had the pins oriented correctly. All you can see is the bottom of the plug from the outside of the amp with the back panel off.

I would like to replace the preamp tube and see if it makes any difference.

Duffy

[tunghaichuan]

You may have to remove the chassis to get to the tubes. Just don't stick your hands inside of it when removing it. There should not be any exposed voltage on the outside of the chassis. In fact, leave the amp on with your guitar pluged into the input. Unplug the power cord and listen to the sound of the amp as the sound fades out. This should bleed of any residual charge. Even if you do this, still, don't put your hands inside the chassis, handle it on the outside only.

The EL84 and 12AX7 use the same tube socket, but have different pinouts. There is a gap in the pins so that the tube will only fit into the socket one way. Make sure you get the right tube in the right socket, you could damage the amp if you don't put them in correctly.

tung




Surfer

I am wondering how you would get out and put in the preamp tube on the V8 without taking out the chasis. I could barely touch it when I was trying to locate it.

How would you line it up to make sure you had the pins oriented correctly. All you can see is the bottom of the plug from the outside of the amp with the back panel off.

I would like to replace the preamp tube and see if it makes any difference.

Duffy

[Spudman]

This sounds like it's built like my VC5212.

If the chassis is mounted to a back board then just remove the board from the cabinet with the chassis still attached to it. That should allow access to change the tubes. No exposure worries other than making sure you don't ping a tube while moving things.

The other option is if you don't have a removable back board then you will have to take the complete chassis off of the cabinet. Still be careful not to ding a tube. They are rather exposed.

Replace the tubes and reattach the chassis. They don't make it easy to get to the tubes, but I have done a tube swap just by reaching up and contorting my body in several strange positions. Not really easy to do and I also bent a pin or two on some tubes so I eventually had to remove the chassis anyway. Mine has 6 or 7 to replace. Yours should be a jiffy job to do.

And like Tung suggests don't go poking around inside the amph and don't let your dogs near it either.

[F_BSurfer]

Just pull the tube straight out when you get the tube clear get a bearing to the direction of the gaps in the pins put the new tube in in the same direction without being forced the tube will only go in one way....take your time

the power tube is held in with screw that holds the retainer on the tube

I'm not pretending to be an amp tech here out of almost 30 years of owning tube amps only the last couple has been working on them just happens I've been inside the v8
Tung has given solid advice on discharging your amp if you find the need to poke around in the chassis take from someone who knows get yourself a pair of chop sticks no fun getting hit

[Duff]

I took it to a really good local tech and he looked at the solder joints and checked everything out.

The tubes were still in great shape and everything was normal. Just typical tube amp hum. I changed around my extension cord and this improved the problem significantly.

What a great little amp tha V8 is, especially when running a Digitech RP350 into it for a major variety of tones. This amp really comes alive and sounds really great.

My Hot Rod Deluxe Tweed with Jensen, however, needed significant work for a brand new amp less than a year old. The first preamp tube was shot and it needed a reverb tank, probably was shot when I bought it new.

Sounds great now, especially with my Epi LP with SD Jazz neck and JB bridge pickups.

So, I didn't injure myself and was careful. The layout of the arrangement is very smartly done to improve safety. The tech definitely did not bias the cathode tube, El84. Supposedly not necessary. The solder joints all looked good.

Duffy

Thanks for all of the safety advice. It was what I needed.