Jansen 12 Sixty head repair

Discuss the stuff that makes your ears bleed.

Moderators: Slowy, Capt. Black

Post Reply
User avatar
MikeC
Vintage Post Junkie
Vintage Post Junkie
Posts: 2938
meble-kuchenne.warszawa.pl
Joined: Fri Sep 12, 2003 5:43 pm
Location: Red Beach, Auckland
Has liked: 1309 times
Been liked: 867 times

Jansen 12 Sixty head repair

Post by MikeC »

Hey all, I have an old Jansen 12 Sixty head that I'd like to repair. I have a schematic drawn out by a guy called Tom Henderson and the first thing I notice is that my amp has 5W/485 ohm "plate resistors" soldered to pin 3 of each of the 4 power tube sockets. The other end of the resistor goes to the OT primary. Usually, pin 3 connects straight to the OT primary. One has seriously smoked (see pic below). These resistors are not shown on my schematic. Any thoughts or ideas on why they are there and indeed if they should be?
Jansen 12 Sixty Plate Resistors.jpg
Jansen 12 Sixty Plate Resistors.jpg (3.89 MiB) Viewed 1975 times
Jansen 12-Sixty Schematic.jpg
Jansen 12-Sixty Schematic.jpg (265.92 KiB) Viewed 1959 times
Whakanuia o mea kei a koe

User avatar
RectifiedAmps
Fender
Fender
Posts: 506
Joined: Tue Jul 22, 2014 7:05 am
Location: Wellington
Has liked: 200 times
Been liked: 240 times

Re: Jansen 12 Sixty head repair

Post by RectifiedAmps »

Do they look original? Your photo suggests as much. I haven’t seen this before but I’ll check to see if I have any 12-sixty photos in my archive. All I can think is that they were there to hobble the output maybe? Strange…

User avatar
MikeC
Vintage Post Junkie
Vintage Post Junkie
Posts: 2938
Joined: Fri Sep 12, 2003 5:43 pm
Location: Red Beach, Auckland
Has liked: 1309 times
Been liked: 867 times

Re: Jansen 12 Sixty head repair

Post by MikeC »

Yeah they do look original. Thanks.
Whakanuia o mea kei a koe

User avatar
sizzlingbadger
Vintage Post Junkie
Vintage Post Junkie
Posts: 8241
Joined: Sat Jan 15, 2011 7:12 am
Location: Wire Wrapper
Has liked: 1203 times
Been liked: 1398 times

Re: Jansen 12 Sixty head repair

Post by sizzlingbadger »

Check the OT resistances, does it look normal for 6L6's ? Maybe they used a different OT and the resistors are there to match the impedance, and would reduce the power output too.
Tube amp and guitar tones straight from 1958… amazing how believable the sounds were back then, even without the modellers...

User avatar
MikeC
Vintage Post Junkie
Vintage Post Junkie
Posts: 2938
Joined: Fri Sep 12, 2003 5:43 pm
Location: Red Beach, Auckland
Has liked: 1309 times
Been liked: 867 times

Re: Jansen 12 Sixty head repair

Post by MikeC »

Good idea - I'll see if I can find out what the typical resistance of the primary would be. I have no way to measure the impedance.
Whakanuia o mea kei a koe

User avatar
Jay
Vintage Post Junkie
Vintage Post Junkie
Posts: 7761
Joined: Sat Sep 25, 2010 9:35 pm
Has liked: 1630 times
Been liked: 1297 times

Re: Jansen 12 Sixty head repair

Post by Jay »

Is it a 6L6 or 6L6GC?
When doing the caculations according to one datasheet from ampage.org, those four 2W resistors are undersized for the GC version and way under for the other. If you must keep them, change to 5W.
When faced with quality, I recognise it every time.

User avatar
RectifiedAmps
Fender
Fender
Posts: 506
Joined: Tue Jul 22, 2014 7:05 am
Location: Wellington
Has liked: 200 times
Been liked: 240 times

Re: Jansen 12 Sixty head repair

Post by RectifiedAmps »

Looks like the earliest Vox AC10s and AC15s had resistors between the anodes and OT primaries as well:
Vox AC15 '59.pdf
(202.13 KiB) Downloaded 85 times
Must’ve been a ‘60s thing :crazy:

User avatar
sizzlingbadger
Vintage Post Junkie
Vintage Post Junkie
Posts: 8241
Joined: Sat Jan 15, 2011 7:12 am
Location: Wire Wrapper
Has liked: 1203 times
Been liked: 1398 times

Re: Jansen 12 Sixty head repair

Post by sizzlingbadger »

Plate Stoppers for stability were a thing.... but they were usually <= 100 ohms.
Tube amp and guitar tones straight from 1958… amazing how believable the sounds were back then, even without the modellers...

User avatar
MikeC
Vintage Post Junkie
Vintage Post Junkie
Posts: 2938
Joined: Fri Sep 12, 2003 5:43 pm
Location: Red Beach, Auckland
Has liked: 1309 times
Been liked: 867 times

Re: Jansen 12 Sixty head repair

Post by MikeC »

Jay wrote: Thu Jun 16, 2022 2:13 pm Is it a 6L6 or 6L6GC?
When doing the caculations according to one datasheet from ampage.org, those four 2W resistors are undersized for the GC version and way under for the other. If you must keep them, change to 5W.
The installed tubes are 7027A - same as 6L6 I believe but some pin-out differences. The pins with the "differences" are not connected on the valve base so no worries there. The resistors are much bigger than 2W resistors - I guessed 5W but don't actually know.
Whakanuia o mea kei a koe

User avatar
MikeC
Vintage Post Junkie
Vintage Post Junkie
Posts: 2938
Joined: Fri Sep 12, 2003 5:43 pm
Location: Red Beach, Auckland
Has liked: 1309 times
Been liked: 867 times

Re: Jansen 12 Sixty head repair

Post by MikeC »

sizzlingbadger wrote: Thu Jun 16, 2022 2:45 pm Plate Stoppers for stability were a thing.... but they were usually <= 100 ohms.
Yeah, it's strange. When I power it up I may do so without the plate resistors and see what voltages I have.
Whakanuia o mea kei a koe

User avatar
MikeC
Vintage Post Junkie
Vintage Post Junkie
Posts: 2938
Joined: Fri Sep 12, 2003 5:43 pm
Location: Red Beach, Auckland
Has liked: 1309 times
Been liked: 867 times

Re: Jansen 12 Sixty head repair

Post by MikeC »

RectifiedAmps wrote: Thu Jun 16, 2022 2:35 pm Looks like the earliest Vox AC10s and AC15s had resistors between the anodes and OT primaries as well:
Vox AC15 '59.pdf

Must’ve been a ‘60s thing :crazy:
Again, interesting, but 100ohm (not 485ohm). I was really hoping to find out how Mr Jansen designed it (Beverley Bruce & Goldie that is)!
Whakanuia o mea kei a koe

User avatar
Anvil Amps Alan
Gibson
Posts: 799
Joined: Thu May 14, 2009 11:52 am
Location: Auckland (Howick)> Paeroa
Been liked: 89 times

Re: Jansen 12 Sixty head repair

Post by Anvil Amps Alan »

I am currently working on a 12 100 which has been seriously molested internally.
Do you have any more gunshots of your chassis which you could share?
"Political correctness is a doctrine, fostered by a
delusional, illogical minority, and rabidly promoted by an
unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end"

User avatar
Slowy
Vintage Post Junkie
Vintage Post Junkie
Posts: 22639
Joined: Wed Sep 09, 2009 4:13 pm
Location: Orcland
Has liked: 1011 times
Been liked: 2466 times

Re: Jansen 12 Sixty head repair

Post by Slowy »

MikeC wrote: Thu Jun 16, 2022 3:12 pm
Jay wrote: Thu Jun 16, 2022 2:13 pm Is it a 6L6 or 6L6GC?
When doing the caculations according to one datasheet from ampage.org, those four 2W resistors are undersized for the GC version and way under for the other. If you must keep them, change to 5W.
The installed tubes are 7027A - same as 6L6 I believe but some pin-out differences. The pins with the "differences" are not connected on the valve base so no worries there. The resistors are much bigger than 2W resistors - I guessed 5W but don't actually know.
The pins are very different. Here's what happens when you don't know this.
IMGP2728.JPG
IMGP2728.JPG (1.25 MiB) Viewed 1433 times
Beyond a critical point within a finite space, freedom diminishes as numbers increase. This is as true of humans as it is of gas molecules in a sealed flask. The human question is not how many can possibly survive within the system, but what kind of existence is possible for those who so survive.

User avatar
MikeC
Vintage Post Junkie
Vintage Post Junkie
Posts: 2938
Joined: Fri Sep 12, 2003 5:43 pm
Location: Red Beach, Auckland
Has liked: 1309 times
Been liked: 867 times

Re: Jansen 12 Sixty head repair

Post by MikeC »

Anvil Amps Alan wrote: Sat Oct 15, 2022 10:25 am I am currently working on a 12 100 which has been seriously molested internally.
Do you have any more gunshots of your chassis which you could share?
No sorry I don't as I sold the chassis to a member here "Optical". He may well be able to assist.
Whakanuia o mea kei a koe

Post Reply