Using An Old Ampeg Tube Head as DI?

[schaf]

I just picked up an Ampeg V-4B head and would like to use it as a DI for my bass. I briefly tried this (plugged the External Amp output into the line input of my interface) and was very happy with the sound, however:

I am concerned that running the amp without anything connected to the speaker output (no power amp load) may be bad for the tubes and/or electronics in the amp.

The output impedance of the "External Amp" output, 10K Ohms, is the same as the impedance of the line input on my recording interface, and the output levels appear to be in a safe range, as long as I keep the volume knob at a reasonable level.

Is there any problem with only running signal out of the "External Amp" output and not the Speaker Outputs?

Thanks!

[Scodiddly]

You really need a load connected to the speaker output. A dummy speaker load would work.

You could try pulling the power tubes if you're just using the line out, but that may throw off the internal voltages a bit by not having their load in the circuit.

[biasvoltage]

That is a good sound, isn't it? But you really need a dummy load.

Operating a tube amplifier without a load attached will cause the output transformer to overheat, short out, and melt. This is one reason to never loan a tube amp to anybody. I found that out the hard way with my 68 bandmaster.

Pulling the output tubes will damage the power transformer. The tubes are part of a circuit, you can't pull those out without causing an imbalance elsewhere in the system.

Get a dummy load! It's the only safe way to do this. I found a 4 ohm metal cased 250w power resistor at a surplus place and used that with an Ampeg V4 for years with no problems. Plus, it looks like the flux capacitor from back to the future, always good to have intimidating stuff like that around the studio.

IF you have the bucks, a VHT hotplate, or a powersoak from Weber or an old Marshall Power Brake is the classy way to go.

[schaf]

Thanks guys! That's what I suspected.

I've got my eyes on this kit:

https://taweber.powweb.com/store/kits_w ... m#loadline

Thoughts on that?

If I did decide to built it from scratch, do I just solder the output of the power resistor(s) to the enclosure? Or would it be better the wire them to the sleeve of the jack?

[Mudcloth]

Thanks guys! That's what I suspected.

I've got my eyes on this kit:

https://taweber.powweb.com/store/kits_w ... m#loadline

Thoughts on that?

If I did decide to built it from scratch, do I just solder the output of the power resistor(s) to the enclosure? Or would it be better the wire them to the sleeve of the jack?

I love Weber stuff. That being said, you could buy a 100 watt wirewound resistor from Mouser for about 12 bucks. Their shipping is a little pricey so I usually load up on whatever other parts I can think of needing until the shipping cost starts to rise in my shopping cart.
http://www.mouser.com/ProductDetail/Arc ... NyDR0LQ%3d

[schaf]

Amazing...I just walked down the street to Austin Amplifier (literally a five minute walk from my house) to ask someone there about dummy loads, and none other than Mudcloth himself was there.

"I need a dummy load so I can use my old tube amp as a DI."

"Is it an Ampeg V-4B?"

"Yeah!"

"You're the guy from Tape Op!"

Small world. Matt has an extra power resistor he's going to sell me so I can rig up a basic dummy load...I'll probably still build the Weber box eventually but this will work for the time being. Those guys are really cool, and super knowledgeable and passionate about vintage amps.

[Producer/Engineer]

Amazing...I just walked down the street to Austin Amplifier (literally a five minute walk from my house) to ask someone there about dummy loads, and none other than Mudcloth himself was there.

"I need a dummy load so I can use my old tube amp as a DI."

"Is it an Ampeg V-4B?"

"Yeah!"

"You're the guy from Tape Op!"

Small world. Matt has an extra power resistor he's going to sell me so I can rig up a basic dummy load...I'll probably still build the Weber box eventually but this will work for the time being. Those guys are really cool, and super knowledgeable and passionate about vintage amps.

That's the coolest thing I've heard in weeks. Ya made me smile!

[AstroSounds]

Oh man! I had one of those heads for a while. Delicious, delicious sound but I needed a live rig amp and that thing just didn't have enough headroom to compete with our loud-as-hell drummer. Wish I had kept it for the studio though.

[Marc Alan Goodman]

Awesome story indeed.

Yeah, V4-Bs are fantastic. I don't know why some people hate on them so hard. When you need powerful muck it's the best amp in the universe.

[ashcat_lt]

An old toaster would work for this. Other ways to do it include incandescent light bulbs and AC motors (like, say, a fan).

I guess it's a bit late, but thought I'd just throw it out there for others who might be wanting to do something like this.

[Scodiddly]

An old toaster would work for this. Other ways to do it include incandescent light bulbs and AC motors (like, say, a fan).

I guess it's a bit late, but thought I'd just throw it out there for others who might be wanting to do something like this.

Unless you have a really high-wattage bulb, it's not going to be in the necessary range for a tube amp.

There are apparently 24-ohm electric water heater elements you can buy at Home Despot and such. Put 3 of those in parallel and you've got 8 ohms. Hang them in a bucket of water and you're good for a few thousand watts disspation.

[Bro Shark]

Another idea is to hook it up to one or more speakers. The bonus is you can point a microphone at them and get a good sound that way.

[Scodiddly]

Another idea is to hook it up to one or more speakers. The bonus is you can point a microphone at them and get a good sound that way.

Oh yeah, right, put a mic on it. That's crazy talk, dude.

[schaf]

Thought I'd post an update...

Matt hooked up the power resistor and it works great. Thanks Matt!

And yeah, I'm definitely going to experiment with micing up the cab as well. I really like the way it sounds in a good room...but it's nice to have both options, especially in less-than-ideal situations.