Palmer DREI – Behind the Scenes (The Marriage)

This video shows the Palmer DREI Triple Single Ended Amplifier in its final production steps. Markus Torvinen (Palmer Engineer) and Robin Henlich (Palmer production manager) opened their doors to show you the marriage of the actual amp and its case. A MUST SEE for all the fans out there.

MARKUS: Okay, I’m testing the DREI amplifier. I take this directly from the assembly guy, and I start testing it. So first I insert the fuses. This is the anode fuse, 500 milliampere, to protect from high voltage. And then I measure… I have a Fluke meter here to measure everything. So first I have to check that I have the correct primary resistance… yeah, it’s good… and then I turn it… I can show you the voltage that I’m getting out. If you’d like to see, this is the operating voltage of the amplifier. I can tell you, please don’t try this at home or at your grandmother’s place.

So now you can see what the operating voltage is… we’re now on 50 Volts, 100 Volts, 200, 300 Volts. I’m doing this very slowly to see if everything is okay, and 555… yeah, this is the operating voltage of the DREI.

And then I adjust the heating voltage for the preamp tubes. The preamp tubes are regulated, so if you see anything like transistors or diodes here inside, that is just to regulate the preamp tube voltage. So now I adjust this to 6.3 Volts.

I leave it a little bit over that because when I put the tubes inside it takes a bit more current, and the voltage goes down a bit.

And the next thing is that I have all the heat-shrink tubing, it hasn’t been shrunk yet because if I see that there’s some problem I don’t have to open everything. So now I shrink the tubes… and I put on a few cable ties. If you’ve wondered why there’s lots of cables and they’re braided, it’s necessary.

Okay, and now I’m ready to put in the tubes. This is the rectifier tube GZ34, and when you change the tubes, please be sure to put them in the right way. This is the power amp tube 6L6, and then I need a 6V6. So before operation you can be sure that we have burned in all the tubes for some hours, and the whole amplifier is burned in for two hours before the playing tests. And this is the tube retainer. I make it a little bit tighter so it’s holding a bit better. And then I put in the preamp tubes, and I make sure that there are no sharp edges and they’re sitting very tightly. So don’t worry that they’re falling out. Okay!

And now I check all the grounds… okay!

Now I know that this amplifier is safe, that I can turn it on with the tubes. So now I check the anode voltage, and you can see that it really needs 20 seconds for the voltage to go up, and that’s because it has an anode choke, and the full anode current is running through this choke, and that’s why it goes up so slowly.

Yeah! This is the operating voltage of the tube, and then I can check the bias current of the different tubes. Yes, everything okay. And then a last check for the heating voltage of the preamp tubes. As you can see one’s a little bit lower. I have to set it a bit higher… yes, this is good. And then I check the other heating voltages. This is for the power tubes. It should be something like 6.5, 6.3. Yeah, okay.

And now I turn this off shortly, and I use contact spray for the pots to run smoothly without any crackling noise. Then I connect the loudspeaker. Always be careful which impedance you connect to this. Be sure to connect a loudspeaker with the right impedance. And then I have the volume full up. Maybe you don’t hear anything because it’s such a low-noise amplifier, but now I start to tickle the parts of the amplifier to see if there’s anything loose. And this is just to be sure that all the parts are soldered, and after this I doublecheck, do it again ’cause you never can be sure. Okay.

And now I will check the basic functions with a guitar. And I can tell you that the functions are very basic because it’s a very basic amplifier.

Alright. This was the tube number one.

And this is tube number two.

And this is tube number three.

Alright. And the different preamp tubes… this is the normal, and this is the high frequency one. Okay!

And now this amplifier is ready for the burn in, final assembly, and for the playing tests, and packing.

ROBIN: So, I’m gonna pack the THREE, the DREI. First things first. I get a nice rag, used to be a bed sheet, some window cleaner with alcohol. You can see that’s highly professional, but it works, works well. Right, next thing is the serial number. It’s 3, 1, 30, 20.

There we go. “Geprüft” means “checked” in German. Alright. So the next thing we need to have on is our grille. As you can see it’s got hinges on it so you can actually flip it down when you want to change your tubes. All the nuts have locking varnish on them, and we’ve got to fasten the hinges with a locking washer in addition. So we’ve got the lid on, looks good, and then I go and get the hood. And now the first thing we’re gonna fasten is the back plate with two screws. So you just have to release two screws if you wanna get to the back, and if you want you can of course also use one of those which you can open by hand. But we deliver that thing with two screws. Okay. I pick it up, flip it over, and the first thing we need to do is do the grounding. There’s a grounding bolt here on the housing, again with a locking washer and an M5 nut. Actually the chassis is only sitting on top now of the back lid so now we’re gonna mount the chassis to the hood. And another grounding lead for the bottom plate… come on there, come on there.

One last look… gonna try if I haven’t screwed anything up while turning it around. That looks good, and we’re just a couple of screws away. So now we’re gonna mount the bottom plate to the chassis and to the hood. As you can see it’s a really, really sturdy construction. And it’s also easy to service should you ever need to service it. I don’t think you would, but as you can see all you have to do is take off the bottom plate. You don’t need to take off any pots or any jack sockets, just the bottom plate, and you’ve got a clean look at the PCB, and you can actually even do service from the top of the amp. You don’t need to take out any of the electronics, and I think that’s a feature that hopefully will never need to be used, but it’s still important and it’s just something Markus, when he developed it, it was important to him because he used to also work as a service engineer, and he knows what a pain in the ass it can be to dismantle a whole amp, find the error, hope to have fixed it, install the whole amp again, power it up and find out that the problem is still there. That’s a pain in the ass. So that’s something we’re avoiding here. You can really work on the amp without having to dismantle the whole thing. There you go, that’s it. Just going to check if all the screws are in, if they’re tight. Nothing’s rattling, nothing’s loose. Give it a bang, see if there’s anything rattling badly. No, that’s just the grille. Let’s see if I can tighten up that screw there. That’s better. Okay.

That’s it! And so now the next step will be… we’re gonna do a power test for two hours. We’re gonna hook this up to a load at full volume, let it get really hot, let the tubes burn in, and after those two hours we’re gonna do a final play test, and then the unit is ready to be packed.

MARKUS: Good morning! Just testing the DREI, and it’s good!

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