A very rare british amp from 1970 : Axis NH-100

[CB Amp]

Hello,

A friend had this amp in his garage for years, and he just decided to have it restored. When he first showed it to me years ago, I had a search on the web and found only one article. But I can't find it anymore. If I remember correctly, Axis amps were hand made by a man near Brighton, and a very few were made. This fellow must have listened to Jimi of course.
This model is a NH-100, 4x EL34, 3x ECC83, S/N 063 and dated 7-70.

The design is not a typical Marshall one :
Aluminium chassis (roughly homemade ! )
B+ after the choke, connected to the outut trans and the screen resistors.
Only 2 grid resistors on the 4 EL34 (on only one tube per side).
2 rather identical channels without cathode follower circuit.
And HUGE transformers !

I just started the restauration (this one needs some work ). If anyone has any information on these Axis amps, I would be happy to know it. Especially if anyone has a photo of the original logo. The dot on the "i" is missing as well as the top of the "s". I would gladly reconstruct it with the most accurate shape.
Thanks.

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[Stevem]

While your at it spin that OT 90 degrees.

[stephen_w_keller]

A few notes are here:

https://www.vintage-radio.net/forum/sho ... hp?t=28068

Unfortunately, the circuit drawing is AWOL.

[Stevem]

After reading those notes I would make a point of doing a simple a low ac voltage driven test of the OT primary to nail down what impedance it is, otherwise your guessing as to what idle current the output tube can survive at.

[CB Amp]

Thanks a lot for your replies !

While your at it spin that OT 90 degrees.

Yes, I did it

A few notes are here:
https://www.vintage-radio.net/forum/sho ... hp?t=28068
Unfortunately, the circuit drawing is AWOL.

Thanks for the link Stephen. I draw the schematic, it's really easy.

After reading those notes I would make a point of doing a simple a low ac voltage driven test of the OT primary to nail down what impedance it is, otherwise your guessing as to what idle current the output tube can survive at.

This thread is a bit weird. At the end the guy says that the amp is finally ok. It must had another problem before. The original wiring is not vey reliable, especially in the PS and power tubes (!).

I entirely rebuilt the amp with a new wiring, good caps, sockets, bias ciruit (the bias pot was a Radiospares one, but pretty crap). It works fine.
The plate voltages are high (565VDC), but it's ok with a good bias adjustement. I would have liked to reduce the B+, but the power trans doesn't allow to choose another winding if we want 6.3V on the heaters.

The first channel is a "bright" one, very crisp and tense. The second one can be called "normal". It's very punchy, and very sweet and mellow at the same time. And it's a powerful amp of course. With less compression than Marshall, and cleaner. It's a pretty good amp !

[stephen_w_keller]

Thanks for the link Stephen. I draw the schematic, it's really easy.

It sounds like an interesting. I'd enjoy taking a look at the schematic, if you care to share it.

Thanks,

Stph

[trobbins]

It can be a joy to eeek out info on such an amp. I have a prototype amp from a local music/service shop made 1964 when young aspiring band members couldn't afford a main label amp so pestered for something cheaper. The background story to that included hearing from a then young guy who recalled the back room where the amps were made, and the shop owner who was more into making the cab woodwork and would use metal handles from the kitchen cupboard trade, and a tolex colour that was the last roll of blue that no one else wanted. The circuit was a dead copy of a Dynaco Mk3. And then out of the woodwork can come photos of the first gigs of young bands, and even a revival gig from old band members using a restored amp - well worth digging!

[Roe]

T
The plate voltages are high (565VDC), but it's ok with a good bias adjustement. I would have liked to reduce the B+, but the power trans doesn't allow to choose another winding if we want 6.3V on the heaters.

Does it have a 240-250v primary?

Doesn't it resemble the Laney Supergroup? (which in turn was based on the jtm45/100 super amplifier but with el34s and partridges)

[TUBEDUDE]

With modern tubes, and a relatively high plate voltage, make sure the screen resistor is sized to well control the current.

[Roe]

Laney used a RS dlx choke with a 690 ohm dc resistance (a choke also used on many marshalls in the 1965-68 period)

[Nate_The_Hieb]

Just dropping in to provide some more information. They were built by a man named Ian Prentice, and they were used by Roger Hodgson and Richard Palmer (the latter having designed the Axis logo) in Supertramp from 1970-72.The amps can presumably be heard on the first two Supertramp LPs.

Along with the NH-100 heads, there were 4x12 cabs (slanted and straight). It appears that they were made in both red and grey. The logo can be seen clearly in the film of Supertramp performing “All along the watchtower” in 1969.