NAD - Jansen Bassman

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Lyle
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NAD - Jansen Bassman

Post by Lyle »

My friend dropped this of this afternoon, it had been sitting out in his shed for a while taking up room.

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Looks in good shape from what I can see through the vents, will have to open it up tomorrow to get a better look.

It's missing a couple of tubes so I need to replace those and see if it runs, then i'll see if I can get the volume above 1!

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Re: NAD - Jansen Bassman

Post by foal30 »

Cool amp

I used one occasionally for recording
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Re: NAD - Jansen Bassman

Post by MikeC »

My first real amp was a Jansen Bassman 75.
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Re: NAD - Jansen Bassman

Post by foal30 »

We had Jansen Amps at high school

Approximately 1986 I purchased a Jansen “Little Brute”
I gigged with a “Crusader” for a bit
Genuine Old Frontier Gibberish

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Re: NAD - Jansen Bassman

Post by foal30 »

This thread has given me an idea for a NEW CONCEPT band
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Re: NAD - Jansen Bassman

Post by Cdog »

They're awesome. A mate has one, sounds really great with guitar or bass. How long hasit been since it was last used? Might be worth getting a tech to look at it before you fire it up the first time.

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Re: NAD - Jansen Bassman

Post by Lyle »

Cdog wrote: Mon Apr 04, 2022 7:03 am They're awesome. A mate has one, sounds really great with guitar or bass. How long hasit been since it was last used? Might be worth getting a tech to look at it before you fire it up the first time.
It's been a few years! I have a friend who repairs hifi tube amps so I'll take it around for him to look at.

It appears to have the 6L6 tubes swapped for for a pair of 7207A which are normally found in the Bassman 75.

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Re: NAD - Jansen Bassman

Post by Anvil Amps Alan »

7027A are like a heavy duty 6L6GC and are likely to be original to the Amp.
You may find that they are still quite serviceable.
A bench test for power output will determine that for sure.
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Re: NAD - Jansen Bassman

Post by Slowy »

Anvil Amps Alan wrote: Mon Apr 04, 2022 9:41 am 7027A are like a heavy duty 6L6GC and are likely to be original to the Amp.
You may find that they are still quite serviceable.
A bench test for power output will determine that for sure.
Don’t 7027s have a different pin configuration to 6L6? I put some in a Flexi 50 and smoke escaped.
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Re: NAD - Jansen Bassman

Post by RectifiedAmps »

Slowy wrote: Tue Apr 05, 2022 7:51 am Don’t 7027s have a different pin configuration to 6L6? I put some in a Flexi 50 and smoke escaped.
7027As have internal connections on pins 1 & 6, whereas 6L6GCs don’t. Sometimes these pins are used as terminal points for screen or grid resistors for 6L6GC designs, so if you use 7027s it’ll produce fireworks.

The schematic for Bassmans actually calls for 6L6GCs *or* 7027s. You don’t see the latter very often though, and I’d guess they were more common in earlier Bassmans.

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Re: NAD - Jansen Bassman

Post by MikeC »

In a 6L6 valve, pin 1 is spare.
In a 7027A valve, pin 1 is internally connected to pin 4 (the screen grid).
So if the amp in question has nothing soldered to pin 1 on the valve base then you should be OK (apart from checking bias).
But if the amp in question has something soldered to pin 1 on the valve base (it's sometimes used as a convenient point for a connection), then smoke may well ensue!
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Re: NAD - Jansen Bassman

Post by Lyle »

It's alive! There's a bit of a low hum that doesn't seem like it should be there but I managed to crank it up without any smoke escaping.

Looking inside there's been some mods made at several stages. Trying to work my way through the wiring schematic to understand what's going on. It's also pretty dusty, I'll upload a photo when I get a chance.

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Re: NAD - Jansen Bassman

Post by RectifiedAmps »

A hum is pretty standard on many Bassmans due to their horrific grounding scheme.

If it helps, here’s a schematic (attached).
Attachments
Jansen Bassman 50 75 6-35 12-60 etc.pdf
(852.7 KiB) Downloaded 80 times

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Re: NAD - Jansen Bassman

Post by Lyle »

Some dusty/rusty looking insides.

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Re: NAD - Jansen Bassman

Post by rickenbackerkid »

Jesus. That could do with a tidy up. I particularly like the new undersized filter caps, wedged in place with bits of mains wire!

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