Off Topic but please help!!

[rychehed]

Hey Guys, this is way off topic but i have an old Ace Tone Mighty-5 amp head from late 60s that ive dusted off recently - but i cant find its Ohm rating anywhere on it...does anyone have experience with these type of amps?...i have heard that most 60s combos and heads were 4 Ohms...

I did unscrew the lid of the head and i saw a pen drawn `4` with what looks like either an Ohm symbol or a `2` - please help guys!! as i havent got a guitar or amp tech anywhere near me!!


Cheers!

[jontheid]

Check here : http://music-electronics-forum.com/t28543/" onclick="window.open(this.href);return false;

The link has a discussion about this amp, with schematics posted.
The schematics show the amp has a single 8 ohm output.

Does your amp have the original 50HB26 tubes?
These are hard to find, but the amp can be converted to run on 6L6s - also discussed in the link.
That said, vaccumtubes.net has 50HB26 listed at $3 each:

http://www.vacuumtubes.net/Prices%2030%20to%20698.htm" onclick="window.open(this.href);return false;

Pretty good value for a NOS 25 watt output tube!

Cheers
Jon

[rychehed]

Check here : http://music-electronics-forum.com/t28543/" onclick="window.open(this.href);return false;

The link has a discussion about this amp, with schematics posted.
The schematics show the amp has a single 8 ohm output.

Does your amp have the original 50HB26 tubes?
These are hard to find, but the amp can be converted to run on 6L6s - also discussed in the link.
That said, vaccumtubes.net has 50HB26 listed at $3 each:

http://www.vacuumtubes.net/Prices%2030%20to%20698.htm" onclick="window.open(this.href);return false;

Pretty good value for a NOS 25 watt output tube!

Cheers
Jon

Thanks alot John for the help! so am i right in reading that 5881s provide a `replacement` to the very hard to find 50HB26 tubes?...unfortunately - i bought the amp with output tubes missing and ive been trying to get hold of these 50HB26 tubes for ages now (these sites saying they have them for cheap really dont have them in stock)...

[jontheid]

Unfortunately there is no easy replacement for 50HB26 tubes.

The 50HB26 is a 50V filament 9-pin power pentode tube using a magnoval base. It has a pretty unique pin-out and nothing else will just slot in and work.

5881s and 6L6s are 6.3V filament 8-pin power pentodes.

To use 5881s or 6L6s you have to fit new output tube sockets, rewire things a bit and also use the preamp tube filament supply for the output tubes. This last bit overloads the power transformer - but the guy who did this on http://music-electronics-forum.com/t28543/" onclick="window.open(this.href);return false; said the transformer coped with it ok.
The other option is to add a dedicated filament transformer for the heaters of the new power tubes.

http://oldtube.com/Oldtube-PriceList.htm" onclick="window.open(this.href);return false; say they have several (11) 50HB26 tubes in stock. The page is in Japanese, but google translates it pretty well. No prices are listed though.

You'd probably need a 300W 240V-100V step-down transformer, that's going to cost about £45. (Even though the amp only outputs 50W, tube amps are incredibly inefficient so you need a transformer much stronger than 50W).

If I were you I would have the amp converted to use modern power tubes. I'd also consider getting the power transformer in the amp changed as well to run directly off 240V so you don't need the step-down transformer.

There is no easy, quick or cheap fix for this amp I am afraid. It all depends how much work and £ you are prepared to put into it.

Cheers
Jon

[jontheid]

Actually looking at the schematic it may be possible that the power transformer in it might be able to work with 240V iif set up correctly internally. Any reasonable tech should be able to open it up and tell you pretty quickly if this is the case. Don't plug it in to UK mains until you have had this checked out though.