Tube Stereo Consoles from Thrift Stores

[kevinkr]

You can't remove the cathode resistor unless you replace it with some form of fixed bias as in batteries or a small negative supply to the control grid. The cathode resistor provides the operating bias for the tube and without bias the tube will quickly die due to excessive dissipation.

Note that eliminating the cathode bypass capacitor will degrade linearity in the midrange and treble as well as reduce the sensitivity.
Given the quality of the output transformer in this design it is unlikely that you can't find a far better quality even electrolytic capacitor... If you are really that phobic about the quality of that capacitor use an inexpensive blackgate and/or try bypassing with a good quality film type.

If you insert nicad/nimh batteries in the cathode circuit normal operating currents will keep them fully charged. Under no circumstances should you ever use an alkaline or conventional carbon drycell as they will leak and quite possibly explode. I can't emphasize this enough.

If you choose to use a negative bias on the grid regular batteries may be employed and these will periodically have to be replaced. (every few years)

[gmilitano]

I finally got around to measuring my 50EH5 project. Attached is the frequency response from 40Hz to 20kHz into 8.2 ohms.

Basically, the amp is -3dB @ 100Hz and about +1dB @ 20kHz.

The response is about what I expected from these tiny OPTs. The plan for this amp is to power a radio shack super tweeter.

Is there any way to measure the response of an output transformer without having it connected to an amp?

Cheers,
Gio.

[Sherman]

Originally posted by GG
I finally got around to measuring my 50EH5 project...

Basically, the amp is -3dB @ 100Hz and about +1dB @ 20kHz.

...The plan for this amp is to power a radio shack super tweeter.
...

Cheers,
Gio.

Gio,
It looks like it would also be good as a "main" amp connected to a subwoofer to supply the low end.

[gmilitano]

Originally posted by Sherman

It looks like it would also be good as a "main" amp connected to a subwoofer to supply the low end.

It would be ok, the problem is I don't have a suitable (efficient) 8 ohm speaker. With the 8ohm 2.5k OPT, this amp sounds horrible into 4 ohms and even worse into 16ohms!

Check out the attached graph.

The volume control will let me adjust the tweeter seperately from the preamp and into an 8 ohm supertweet @ 97dB, the low power is not an issue.

Cheers,
Gio.

[planet10]

Originally posted by GG
about +1dB @ 20kHz.

The rise in the top may well be a sign of some ringing in the OPT... adding an appropriately sized (small) cap shunting the primaries is a tactic often used to counter this.

dave

[Geek]

Originally posted by GG
When I go to a thrift store, there is almost always an old Tube Stereo Console available for $7 to $25 CDN.

You are sooooo lucky!!!!!

The thrift stores in Abbotsford/Chilliwack *know* what they have and price accordingly

[wrenchone]

I just picked up the radio portion of a Sears console on fleabay. It sports a pair of single ended output amps using 25F5s It's all series string with a "sudden death" non-isolated chassis. I was thinking of refurbing this thing with an isolation transformer (a 50-100VA isolation transformer is cheap locally) and various improvements and dropping it into a wood box with some open baffle arrays. I have a bunch of oval Samsung TV speakers that may be just the thing it needs to see.

[CrazzyAbtTubes]

I have A Grundig stereo console like the one shown at the beginning of this thread, I don't have a clue how to wire up the output but it looks to be in very good shape.

All the parts and tubes are there including the cable & plug for the speakers that would have been inside the cabinet, but I still only have the console.

Does anyone have a diagram or output wiring suggestions so that I can hook up a pair of 8 ohm speakers to test the console?

[nacho1966]

Originally Posted by gmilitano

For interests sake, here is the Viking with ECL86

BTW - what is an RH Circuit?

Gio.

Hi,
I know this message is around 6 year late, but I knoticed the console Viking ECL86 amp pic the other day and it appears to be the same amplifier that I recently pick up. Like you, I had pick it up next to nothing and I was hoping to use it as my introduction to the world of diy. I do have a couple of questions that I was hoping you may be able to help me with.

I'm not actually clear who manufactured it as it doesn't seem to indicate. Would you know the manufacturer and model number. Is it worthwhile converting this into a stand alone tube amplifier. What would the power rating be for it. Any ideas as to where I can get my hands on the schematic.

Lastly, did you end up doing anything with the one in the pic.

Thanks,

[planet10]

Viking was an Eatons house brand. They'd contract a furniture maker to make the consoles, and those would buy amplifiers from an OEM. Even if we knew who, their name probably wouldn't be recognizable.

dave