Hiwatt AP CP103 ,2005 valve amp

[N_Cook]

Blown mains fuse and owner thinks he replaced the HT and mains ones after
initial failure.
Amp failed in tune 5 into a gig , playing loud but normal for this amp (does
"The Who" front label make it louder?) and fuse/s blew. Next day, he has a
1970 Hiwatt L 100W Mark 4 ? M41.. serial number anyway, and according to the
owner very rare, this one should be ok when it gets 4 EL34 valves again.
One of the 2005 EL34, the getter was white so he threw it out ,
unfortunately . I'm out of contact with him for a couple of days but looks
as though the other of one of the side pair was partially white and kept
this one same make and appearance as the others in the amp, now mixed in
with his box of untested valves. Anyway in the end he robbed 2 EL34 from the
working vintage one and still blew fuse/s.
All Rs look and measure ok in the PA section. Powered up with 70 percent
mains with no output valves, only prea ones , and voltages seem right for
that mains including bias voltage. Tx resistances seem normal.
This part white EL34 , 2/3 white , 1/3 mirror Cs getter, blown heater. The
vertical rod electrically attached to p1 , G3 , but physically on the other
side of the valve electrically connected by the top "halo", electrode is
discoloured to blue compared to the other valves. No obvious cracks , I
suppose deliberately breaking it will confirm was still functional getter.
But something coming off the rod reacting with the getter while hot and not
fully converted to a white form ?
Won't be testing them and his other "spares" until tomorrow.
One 8 pin black socket (marked Made in Italy , EF ?) is discoloured to dusty
grey appearance around pins 2,3 and 6, 6? no pin in that one ?.
Trying a 2.2mm drill shank (not the cutting end) it is close sliding fit to
the old amp socket pins but slack sliding fit for the 2005 one
Measured a few EL34 pin diameters, p1 and 8
2.22, 2.31 mm
2.26,2.30
2.18,2.33
2.26,2.30

EL24 from the 1970 amp
2,41,2.41 mm
2.40, 2.46

so suspect contacts in the sockets? and loss of bias voltage ?
Retaining springs for the new version , not considered necessary in the the
old one

 

[Jamie]

Blown mains fuse and owner thinks he replaced the HT and mains ones after
initial failure.
Amp failed in tune 5 into a gig , playing loud but normal for this amp (does
"The Who" front label make it louder?) and fuse/s blew. Next day, he has a
1970 Hiwatt L 100W Mark 4 ? M41.. serial number anyway, and according to the
owner very rare, this one should be ok when it gets 4 EL34 valves again.
One of the 2005 EL34, the getter was white so he threw it out ,
unfortunately . I'm out of contact with him for a couple of days but looks
as though the other of one of the side pair was partially white and kept
this one same make and appearance as the others in the amp, now mixed in
with his box of untested valves. Anyway in the end he robbed 2 EL34 from the
working vintage one and still blew fuse/s.
All Rs look and measure ok in the PA section. Powered up with 70 percent
mains with no output valves, only prea ones , and voltages seem right for
that mains including bias voltage. Tx resistances seem normal.
This part white EL34 , 2/3 white , 1/3 mirror Cs getter, blown heater. The
vertical rod electrically attached to p1 , G3 , but physically on the other
side of the valve electrically connected by the top "halo", electrode is
discoloured to blue compared to the other valves. No obvious cracks , I
suppose deliberately breaking it will confirm was still functional getter.
But something coming off the rod reacting with the getter while hot and not
fully converted to a white form ?
Won't be testing them and his other "spares" until tomorrow.
One 8 pin black socket (marked Made in Italy , EF ?) is discoloured to dusty
grey appearance around pins 2,3 and 6, 6? no pin in that one ?.
Trying a 2.2mm drill shank (not the cutting end) it is close sliding fit to
the old amp socket pins but slack sliding fit for the 2005 one
Measured a few EL34 pin diameters, p1 and 8
2.22, 2.31 mm
2.26,2.30
2.18,2.33
2.26,2.30

EL24 from the 1970 amp
2,41,2.41 mm
2.40, 2.46

so suspect contacts in the sockets? and loss of bias voltage ?
Retaining springs for the new version , not considered necessary in the the
old one

If it's any thing like the EDM machines I used to work on years ago
that used 4-400Z tubes, the power supply caps get bad and when the amp
is under heavy load does not get sufficient power. THis also means the
bias circuit maybe lifting and causes the tubes to start cutting in DC
current and over heating.

It was common to see these tubes glowing a mild orange color when
they were fully working properly however, a bright orange or worst, near
white is a not so good.

You need to put a load on the amp, test signal, DMM and scope to
monitor the B+ and bias voltage under max load.

A lot of times the large caps may test ok for capacitance but have
leakage. This leakage, as small as it could be can add extra load on the
supply and thus the valves as you say (tube) circuit suffers at the
high end along with having ripple that may not be explainable.

ALso, high freq oscillation can cause unexplained over heating and can
be seen on the scope. THis usually is due to a small cap+R circuit that
has failed in the circuit to neutralize the effect.

Today we work on machines that employ a single oscillator tube that
pumps out at the plate around 275k watts. It's water cooled, the heater
is operated from a 12 volt AC 250 amp transformer and the simplest form
of thermal protection ever devised is a piece of nylon/plastic fishing
line tied to a post in the center of the tube assembly back to a wall
mounted whisker switch actuator arm. If the temps are high enough to
melt that line it simply breaks and the switch shuts things down.

That operation uses a hot cathode triode and the heater element is
made of compressed sheet metal which is also the cathode. THey make nice
lamps when their service is no longer useful

Jamie

 

[N_Cook]

The Italian sockets are maybe marked EE, anyway socket pins are now strong
sliding fit to 2.2mm drill shank.
Curvey Es like the E of the compliance CE controlle european mark, maker
name not found Googling
The 1970 amp is marked Sound City "one hundred" on the gold fascia panel.
Suspiciously small 63V 100uF bias cap replaced with 100V one in the 2005
amp.
O/p Tx tests good balanced with reverse feed AF sig gen.
Anyway with valve testing can be pretty sure of the "etiology" .
Both these amps are stored in the same unheated warehouse, the newer amp
looks far worse from internal corrosion, than the 1970 one.
Poor socket pins and corrossion on the valve pins lead to loss of bias. Then
owner robs a pair of valves from the good amp , but one of those valves has
a broken polarising nib. Tracing back to my markings on receipt this valve
was rotated one position out in the base, the one position that connects
anode to
cathode via the heater.
The old valve pins showed no corrossion but the recent JJ ones had bad grey
dust corrossion , leaving large grey deposits on cosmetic nail sanding
boards.
One valve tested on my Avo as no heater and took a lot of abraiding to the
pins to get
the heater current through. Another one tested as no gain until I repeated
the sanding.
The JJ valves had no date mark just an E in a cartouche. And marking
N5LN5
datecode for 2005 ?
I don't think the pin infil is PbF, but has the bright tin tinning of the
pin surface turned to tinpest? - those grey patches were certainly
insulating to 30M , DVM anyway.
As a puzzle for anyone with the inclination. If the valve with the broken
nib was placed in the socket with perhaps overheating marks in the bakelite
of pins 2,3 and 6 what orientation would lead to serious overheating at
those pins?
The heater chain on these amps uses "dummy" socket pin 6 as a resistor tag
from HT2 supply, EL34 are NC and usually NP for pin 6

 

[N_Cook]

It's not really an 'electrode' as such - as in a functional part of the
valve. It's the 'trough' in which the gettering material, often magnesium,
is deposited at the time the valve is built. After the envelope has been
evacuated with the vacuum pump and sealed off, the whole assembly is
subjected to an intense (RF?) field. The 'halo' as you call it, acts as a
shorted turn and heats to the point where the gettering material is 'fired',
eating up the remaining air traces, and locking them in the splatter that
deposits itself on the inside of the glass - the brown mirror that indicates
that the vacuum in a valve is still good. If air gets in, the deposit turns
to white magnesium oxide, and is a clear indicator that the security of the
vacuum has been compromised.

Arfa


is

I went to test that part failed one yesterday and over a couple of days it
had turned fully white, must have been a very tiny leak/self-stopped,
handling was enough to make it open up a bit

 

[N_Cook]

Back working again, I'm still trying to find the maker of those Italian
valve sockets if anyone has any ideas.