EL821/6ch6 amp

[Alex R]

I have this old early 60s brit amp in for a rebuild. It's actually called a Dallas Rangemaster, but I assure you it's an amp, not a pedal. Preamp is 2 x EF86, one per channel, and something else that looks like one of those half-triode half-something else 12AX7 sized things. Well I'll figure that out as the valve is actually present. The power amp is separate inside the cab. It has an EZ81 rectifier, and empty sockets for a splitter and two power valves, all 9-pin. Someone has written EL84 by the power valve sockets but that must be wrong as they are wired this way:

pin 2 signal/bias
pin 3 and 9 cathode resistor
pin 7 plate supply
pin 8 screen supply

This would I reckon work for EL821/6CH6 valves. I have a recollection of other brit amps of the period using them so they are my prime suspect; I've even ordered a NOS pair as they are cheap and easy to get.

Questions: Do you think I'm right about the EL821? And what about the splitter? It looks like a LTP but the only circuit I can find on the web uses two 6C4 (which can't be right for this amp as it's a 9-pin socket) - would a 12AT7 work in this amp? About 10mA of plate current, bit like a 6C4? Would that drive 2 x EL821? All speculation gratefully received however vague - but I would be extremely grateful if anyone had direct experience of these little rarities.

[Alex R]

...for the record, this little amp came together really nicely. Dallas Rangemaster, preamp has one EF86 per channel feeding into a TB tone stack and one shared half of an ECC83. On the separate power amp chassis an ECC83 splitter feeds 2 x EL821, which are readily and v cheaply available as NOS Mullards and seem to be beam tetrodes in EL84-ish bottles. EZ81 rectifier. The speaker has a light bulb limiter on it. Lots of crunchy gain and what with the light bulb and all, compression too. Never saw a light bulb on a speaker before.

[cservonyec]

Alex
I had the chance to rebuild another Rangemaster amp, exactly like this: http://www.vintagehofner.co.uk/amps/dall15.html When I got the amp I was stupid not to draw the schematic before I cannibalised it for another amp. I've only sketched the power section. Later I tried to put it back togeather, and found no documentation on the net. Eventually I've tracked down the gentleman, who posted the picture of the above amp. He kindly let me have a look at the amp and I took photos of it, he also sent some pictures via email, that he took from the inside. The power amp section (mine!) had a cathodyne and not a long tail phase splitter. Also it had an additional EF86 for the tremolo section. This gave me lots of head aches to figure out the schematic. Eventually used the one from the vox ac10 circuit, as all the resistor values, and layout seemed to match. By the way it also had a light bulb, but it made no difference if I took it off. The power tubes were Brimar 6BW6. These are actually 6V6 tubes in a 9pin miniature body! This amp rocks. Real early british sound with a lovely early break up warmth. I've sold it to my wife's brother's son.

[Alex R]

That's the one, very neat little amp. And they do sound good. No I didn't trace out the circuit either.

EL821 and 6BW6 seem to be similar general types, haven't looked at the pin-outs.

Cathodyne phase inverters do sound good for guitar I think - Princeton, Superchamp, Peavey Classic/Delta Blues, all have really sweet cleans which I guess may be produced by the slight imbalance in the PI.

[cservonyec]

I am really glad I've found this forum. It is exactly what I was looking for. I've got some of the original pictures of the inside of this amp if anybody interested, let me have your e-mail address and I will post them.

[cservonyec]

Dallas Rangemaster amp

Alex. Do you still have this amp, or access to this amp.
The tubes by the way if it is the same amp I am thinking of are:
two EF86 for each preamp section, one ECC83 for (just half is used) to drive the tonestack, one EF86 for the tremolo section, one ECC83 for the phase splitter and two 6BW6 pentodes, that are the miniature versions of the octal 6V6GT.

If you have a way of contacting the person who owns this amp, can you ask him to get in touch with me, as I desperately need the schematic for this amp.
I've loaded some pictures on this forum:
http://music-electronics-forum.com/s...ad.php?t=10117
My email address is: laszlo@greenamazon.f9.co.uk
Thanks.

[Alex R]

long gone out of the shop and forgotten I'm afraid...

[cservonyec]

Dallas Rangemaster amp

Not to worry Alex. If you ever come across with one of those, would you let me know please?
Rock on.
L.

[Alex R]

I will. The one I had in looked completely different from yours though.

[cservonyec]

Dallas Rangemaster amp

Yeah, these are rare as hen tooth. The only circuit I am really interested in these are the tremolo and the tone stack. Both were kind of strange. The tone stack was like a bandaxall type, but with some extra components, and the tremolo section was just like the AC10's but somehow not cathod coupled. Either anod or screen grid coupled if that is possible. I tried to recreate it from the values I knew and from the pictures I have, but couldn't get it working yet.
So the search goes on. Someone must have these amp somewhere in the world, as they come up on ebay now and then.
L.

[Ian_1969]

Yeah, these are rare as hen tooth. The only circuit I am really interested in these are the tremolo and the tone stack. Both were kind of strange. The tone stack was like a bandaxall type, but with some extra components, and the tremolo section was just like the AC10's but somehow not cathod coupled. Either anod or screen grid coupled if that is possible. I tried to recreate it from the values I knew and from the pictures I have, but couldn't get it working yet.
So the search goes on. Someone must have these amp somewhere in the world, as they come up on ebay now and then.
L.

Hi,
I have two Dallas Rangemaster combos with twin 10" celestion speakers dating back to early 60's. One amp is in mint condition and has been mothballed for over 4 decades so is a good as the day it left the showroom floor, the other is still in great shape. Both amps play well. I have all the original parts and valves still in them so I guess with cross-referencing between the two a very accurate circuit is possible.
The amps looks like this model:
http://www.vintagehofner.co.uk/brita...f/dall11a.jpeg
I have been meaning to draw the circuit but may need some help with how to do that. ( software to use and any other tips)

[Alex R]

That doesn't look like the one I had in at all. Mine was this version: Dallas Rangemaster Model 5411/5412 Amplifier

[cservonyec]

Hi,
I have two Dallas Rangemaster combos with twin 10" celestion speakers dating back to early 60's. One amp is in mint condition and has been mothballed for over 4 decades so is a good as the day it left the showroom floor, the other is still in great shape. Both amps play well. I have all the original parts and valves still in them so I guess with cross-referencing between the two a very accurate circuit is possible.
The amps looks like this model:
http://www.vintagehofner.co.uk/brita...f/dall11a.jpeg
I have been meaning to draw the circuit but may need some help with how to do that. ( software to use and any other tips)

Don't worry about software, all you need is a pencil or pen then when it is complete, then scan it with a scanner and post the picture of it. The software is too fiddley. If you don't know the values of resistors, then just note the colours of the rings on them. You don't even have to have the schematic, just the layout will do, as we can draw the schematic from it.
Good luck.
By the way here is a picture of a Triple Tone Amp, and my dallas rangemaster had exactly the same chassie, down to the tee, transformers, and the printed circuit board identical, so there is a connection between these amps. Of course the dallas's preamp was on a separate panel, but they must have shared the same power amp section. Even the meticilous quality of the wiring, layout is identical. Here is a link to it:
6V6 G TRIPLE TONE VALVE MONO AMPLIFIER + spare valves on eBay (end time 06-Feb-10 08:54:36 GMT)

This is for Alex to verify that I am right?!!

[Ian_1969]

Ok been so long since I was on here. I am altogether too busy but now on holidays so may finally get a chance to do the world's only schematic of an early 60's Dallas Rangemaster 2x10" tube combo.

[cservonyec]

Ok been so long since I was on here. I am altogether too busy but now on holidays so may finally get a chance to do the world's only schematic of an early 60's Dallas Rangemaster 2x10" tube combo.

Just do it man, don't wait another 6 Months. Get a pencil, a sheet of paper and draw it.
Best way to approach it is to draw the components and where do they go, which pin or lag it is connected to. Then from your raw drawing work out the schematic.
Good luck!