Can I use this stuff (does it have any value?)

[carter840]

So I have been curious about building my own guitar amp and have heard great things about tube amps. I am low on cash and can't justify spending the money on a tube amp so I was wondering If I could build one. I am an engineer and am quite certain I could handle the schematics and soldering etc.

That said it seems like even building your own tube amp can be expensive. At my Mother's home I found an PA system in a cabinet that is quite old, it doesn't work (or isn't hooked up anymore at least) and she said she would be happy to let me have it. It has probably been there since the 50's before she bought the house and I was wondering if any of the components might be worth something or the unit as a whole. I am thinking either I could use one of the tube amps on here to build an amp or sell some of the parts (or the whole unit) to fund my project.

Any help would be appreciated. I am attaching pictures to this post.

Great forum- I look forward to learning from you all
Thanks

[dcgillespie]

That unit would certainly serve as a great platform to build a guitar amp from -- the transformers, tubes -- almost all of it. You would really only need to provide a suitable preamp to drive this unit with, that has the proper eq for guitar amp service. You would want to make sure it has an appropriate output tap for the speaker(s) you plan to use. I would restore the Executone to full, dependable working conditon, and then build your little preamp to complete the project. There appears to be enough tube sockets already on that chassis already to convert one of the small 9-pin tubes to a conventional preamp circuit. The existing circuit likely provides more gain than is necessary for a typical guitar preamp, so that one could be converted to that service.

Dave

[Soonerorlater]

Might need to check it can drive an ordinary speaker (4/8/16 ohm).

Valves look "tasty"..........


ps was there a speaker with it.

[v4lve lover]

hell yeah if it has taps for your speakers . tubes are6550 and 12ax7 /12au7 probably PP

if it has good secondairy taps it will work like a charm .
google the chassis name/brand ect to find out what it was originaly designed for .

if OPT is good and tubes in decent condition you could be looking at a 20 dollar parts list .

first undo the screening cans on that other tube and let us have a glance . :rolleyes

there is probably a good scematic on the internet . whit a 6550 PP guitair amp whit 12au7 phase splitter and 12ax7 front end .

and yes it can definetly be modified to be used as a guitair amp . you should first try to get it working though

[carter840]

Hi all,

First thanks so much for the fast and helpful replies.

I am a complete Noob at DIY audio, and frankly am a little overwhelmed, but excited. I will be at my mother's house this weekend and will work to remove this unit. I am a little concerned about getting electrocuted while removing this stuff since all of that old electric is abandoned and although probably dead I am still a little perturbed.
As for the speaker there is a this (see picture) located next to the Amp. I am not near this stuff right now so I can't get anymore info, but it doesn't look like a great speaker, or is it?

I will look around the house for other stuff this weekend. At one point I think the entire house (large house) was wired with an intercom and I have seen a few speakers around the house that might be good. I feel like I am on a treasure hunt right now. The only problem is I can't tell tin from silver and that is why I need your help.

Also I don't have a picture of it, but I think there is a smaller amp next to this one with only a couple of tubes coming out of it.

Once I get all of this stuff disconnected is there a quick way to test it? Also is there a certain way I can disconnect this to ensure that I do not destroy any value that these components might have. Perhaps their are special wires that connect these components? My guess is that the tubes and guts are what is important, but before I go cutting wires I wanted to double check. Also perhaps I could test this in place before removing it?

I also have a friends who has a pretty new guitar amp that broke, it was a very expensive amp and I think it was tube based maybe I can use that speaker?

[boywonder]

Carter: One thing......resist the urge to power up this equipment as soon as you get it on the bench, as ancient capacitors that have not been fired up in decades can instantly self distruct/explode taking other components with them. The B+ voltage on this amp is probably 400-500V or so.

If the amp looks complete, you need to do a few checks with a multimeter (first with the tubes out, then a few more with the tubes reinstalled).

Ideally, if you can get your hands on a variac, that's the best way to bring up the voltage slowly upon first power-up. If you cannot use a variac, do a search here in the tubes forum for the lightbulb in the power cord trick.

There are plenty of folks here that can help you get this powered up safely, just take your time.

Do you have access to a tube tester? That's another handy thing for getting started.

[carter840]

I don't have access to anything really I can certainly borrow a multimeter from work. But I don't have a tube tester, Oscilliscope, or even know what a variac is. I have been reading some of the info in the newb sticky in this section, but still lack the knowledge I will need.

I guess at this point my plan is to take the speaker, the amp I have shown in the picture aswell as box that is nearby that has two tubes sticking out of it. Once I get them down I will be posting a bunch of pictures and with your help we can see exactly what I've got.

I did do some research on this amp the Executone Model PB-535. I haven't found anything about this particular model, but there was a post on here about a 25 Watt model. The one I am looking at is 35 Watts. Here is a link to that thread:
http://www.diytube.com/phpBB2/viewto...ca3442efe4749f

It doesn't seem like that one had much value, but then again it didn't have all the tubes in place. I am guessing that this was for an intercom and/paging system in the house back in the 50's or so.

[boywonder]

Here is a rough summary to get started, assuming the amp is complete:

Do a search and try to find a schematic....post here if required, someone may have something close.

An O'scope is very handy for this, but not required. Same with a variac. Search for the lightbulb in the power cord trick if you can't get your hands on a variac.

Cut off the 2 prong power cord, install a grounded power cord and tie the cord ground to the chassis using a ring lug and a star lock washer. Convince yourself that the chassis is grounded well by checking the resistance from the ground prong to the chassis metal.

Solder a 220K-470K ohm 2W or larger (anything between these will work fine also) across the power supply cap to bleed down the high voltage when you turn off the amp. There may (or may not) already be a bleeder R in there; if you get a schematic it will be obvious. You may end up replacing the old cap, but put a bleeder R across it anyway for testing, it's cheap insurance.

The above two things are for safety and keeping yourself alive.......also read the safety sticky in the tubes forum.

Also highly recommended even if you are broke.....buy a set of clip leads for your meter. That way you can test "hands free". If you need to probe a live amp, ALWAYS KEEP ONE HAND IN YOUR BACK POCKET. That avoids taking B+ voltage across your chest/heart when you use both hands.

Determine if the amp has a tube rectifier or uses solid state rectification.

With the amp UNPLUGGED, check resistance from one side of the power supply cap to ground. One side of the PS cap is grounded, and the other should be very high resistance to ground. If not, you've got a short somewhere which will need to be fixed before powering up. There may be more than one PS cap, but one side of the PS caps are at B+ voltage and the other side will be grounded.

Pull the tubes and check them on a tester if available.

Connect a large wattage 8 ohm resistor across the 8 ohm speaker taps (or a 4 ohm R across the 4 ohms taps, etc.) Ideally a sand type power R with 25W rating rating will be sufficient. This keeps the HV in the amp from exceeding the dielectric strength of the output transformer windings and cap voltage when applying mains voltage. Never apply full mains voltage to a tube amp without a proper load on the speaker terminals.

If you get this far, let us know, and we'll post the next steps.......

[boywonder]

Your amp is probably very similar to the amp in your link. It may not be HiFi but will work fine as a guitar amp. The one in the link uses tube rectification (5U4)...your amp may have the same rectifier tube.

You can plan on needing to replace a few capacitors once you get the amp on the bench. Modern caps are cheap and robust. Old leaky caps can cause lots of hum and other problems....even if they survive the re-forming process at first power-up.

If the iron is good and the tubes have some life left, you may be able to resurrect this amp for little $$.

The amp in your link uses PP 6L6's for 25W; your amp is PP 35W.........as mentioned possibly PP 6550's.....

[K.A.B]

Take a look in the chassie maybe there are the schematic for your amp this was common to do that from many of the manufactures.

Anders