[Gareth Magennis]

Hi,

trying to find a schematic for an Orange PA200 or OR200 amp, the ones with 4
x KT88's. Doesn't have to be exactly the right one but 4 x KT88's would be
a good start.



Thanks,



Gareth.

[Eeyore]

Gareth Magennis wrote:

Hi,

trying to find a schematic for an Orange PA200 or OR200 amp, the ones with 4
x KT88's. Doesn't have to be exactly the right one but 4 x KT88's would be
a good start.

I recall working on one of those. Does it have individual bias pots ?

Graham

[Gareth Magennis]

"Eeyore" wrote in message
...


Gareth Magennis wrote:

Hi,

trying to find a schematic for an Orange PA200 or OR200 amp, the ones
with 4
x KT88's. Doesn't have to be exactly the right one but 4 x KT88's would
be
a good start.

I recall working on one of those. Does it have individual bias pots ?

Graham



Yes it does indeed, one per tube, and about 720 volts on the first cap with
no valves in. One hand is in my pocket.


Gareth.

[Eeyore]

Gareth Magennis wrote:

"Eeyore" wrote in message
Gareth Magennis wrote:

Hi,

trying to find a schematic for an Orange PA200 or OR200 amp, the ones
with 4
x KT88's. Doesn't have to be exactly the right one but 4 x KT88's would
be a good start.

I recall working on one of those. Does it have individual bias pots ?

Graham

Yes it does indeed, one per tube, and about 720 volts on the first cap with
no valves in. One hand is in my pocket.

The HT is pokey in those. I once got a zap from some HT caps that either didn't
have a bleed resistor or had a very high value that took forever to discharge
them in an amp with a similar supply and it made a tiny hole in the end of my
finger !

I don't have a schematic, I just worked ny way round it as you do.

It was an impressive repair job btw. A 'roadie' had disconnected the speakers
while the bass player was tuning up and there was a nice light show from the
interior. I think the O/P transformer went u/s and 4 new KT88s were needed as
well.

2 of the KT88s had taken so much current that the anodes had actually started to
*MELT*. I even still have them ! If I can find them I'll post a pic in a.b.s.e.

Graham

[Joseph Meditz]

Eeyore wrote:
Gareth Magennis wrote:

"Eeyore" wrote in message
Gareth Magennis wrote:

Hi,

trying to find a schematic for an Orange PA200 or OR200 amp, the ones
with 4
x KT88's. Doesn't have to be exactly the right one but 4 x KT88's would
be a good start.

I recall working on one of those. Does it have individual bias pots ?

Graham

Yes it does indeed, one per tube, and about 720 volts on the first cap with
no valves in. One hand is in my pocket.

The HT is pokey in those. I once got a zap from some HT caps that either didn't
have a bleed resistor or had a very high value that took forever to discharge
them in an amp with a similar supply and it made a tiny hole in the end of my
finger !

I don't have a schematic, I just worked ny way round it as you do.

It was an impressive repair job btw. A 'roadie' had disconnected the speakers
while the bass player was tuning up and there was a nice light show from the
interior. I think the O/P transformer went u/s and 4 new KT88s were needed as
well.

2 of the KT88s had taken so much current that the anodes had actually started to
*MELT*. I even still have them ! If I can find them I'll post a pic in a.b.s.e.

Graham

Hey Graham,

Would you happen to know the impedance of the OT of an Orange OR 80?

I've never played through an Orange. I've only seen pictures of them,
such as on the Orange Field Guide website. They look righteous! Check
out the workmanship on that Custom AD50.

http://www.orangefg.com/

Joe

[Eeyore]

Joseph Meditz wrote:

Eeyore wrote:
Gareth Magennis wrote:
"Eeyore" wrote in message
Gareth Magennis wrote:

Hi,

trying to find a schematic for an Orange PA200 or OR200 amp, the ones
with 4
x KT88's. Doesn't have to be exactly the right one but 4 x KT88's would
be a good start.

I recall working on one of those. Does it have individual bias pots ?

Graham

Yes it does indeed, one per tube, and about 720 volts on the first cap with
no valves in. One hand is in my pocket.

The HT is pokey in those. I once got a zap from some HT caps that either didn't
have a bleed resistor or had a very high value that took forever to discharge
them in an amp with a similar supply and it made a tiny hole in the end of my
finger !

I don't have a schematic, I just worked ny way round it as you do.

It was an impressive repair job btw. A 'roadie' had disconnected the speakers
while the bass player was tuning up and there was a nice light show from the
interior. I think the O/P transformer went u/s and 4 new KT88s were needed as
well.

2 of the KT88s had taken so much current that the anodes had actually started to
*MELT*. I even still have them ! If I can find them I'll post a pic in a.b.s.e.

Graham

Hey Graham,

Would you happen to know the impedance of the OT of an Orange OR 80?

No but it wouldn't be hard to calculate.


I've never played through an Orange. I've only seen pictures of them,
such as on the Orange Field Guide website. They look righteous! Check
out the workmanship on that Custom AD50.

They've always been in top league of guitar amplification.

Graham

[Gareth Magennis]

"Eeyore" wrote in message
...


Gareth Magennis wrote:

"Eeyore" wrote in message
Gareth Magennis wrote:

Hi,

trying to find a schematic for an Orange PA200 or OR200 amp, the ones
with 4
x KT88's. Doesn't have to be exactly the right one but 4 x KT88's
would
be a good start.

I recall working on one of those. Does it have individual bias pots ?

Graham

Yes it does indeed, one per tube, and about 720 volts on the first cap
with
no valves in. One hand is in my pocket.

The HT is pokey in those. I once got a zap from some HT caps that either
didn't
have a bleed resistor or had a very high value that took forever to
discharge
them in an amp with a similar supply and it made a tiny hole in the end of
my
finger !

I don't have a schematic, I just worked ny way round it as you do.



Well I'm just poking around at the moment making sure everything is OK,
which it isn't, and that I am not going to die in the process. The bleeders
are all intact and eveything is safe in a minute. I learnt my big lesson on
an Ampeg with one hand holding the chassis. Very unpleasant indeed.




Gareth.

[Joseph Meditz]

Eeyore wrote:
Joseph Meditz wrote:

Eeyore wrote:
Hey Graham,

Would you happen to know the impedance of the OT of an Orange OR 80?

No but it wouldn't be hard to calculate.



How?

[Joseph Meditz]

Eeyore wrote:
Joseph Meditz wrote:

Hey Graham,

Would you happen to know the impedance of the OT of an Orange OR 80?

No but it wouldn't be hard to calculate.


How? I don't have the transformer in front of me.

Joe

[Eeyore]

Joseph Meditz wrote:

Eeyore wrote:
Joseph Meditz wrote:
Eeyore wrote:
Hey Graham,

Would you happen to know the impedance of the OT of an Orange OR 80?

No but it wouldn't be hard to calculate.

How?

From the rated power ( turn that into volts ) and the voltage swing at the
anodes. That gives you the turns ratio.

The primary impedance is just the square of the turns ratio times the load
impedance.

It seems too much fuss is made over trying to make this tricky.

Graham

[Eeyore]

Joseph Meditz wrote:

Eeyore wrote:
Joseph Meditz wrote:

Hey Graham,

Would you happen to know the impedance of the OT of an Orange OR 80?

No but it wouldn't be hard to calculate.


How? I don't have the transformer in front of me.

You don't need it.

Graham

[Phil Allison]

"Joseph Meditz"


Would you happen to know the impedance of the OT of an Orange OR 80?

No but it wouldn't be hard to calculate.


How?


** Just using Ohm's law and a few simple approximations. The amp is push
pull so the DC voltage ( around 700 volts at idle we are told ) is applied
to the CT of the OT. The amp used 4 x KT88s ( real GEC ones) so the output,
with 700 volt supply, should be 200 watts rms or a little more.

Now, the plate voltage on each pair of KT 88s will swing from a low of about
90 volts to a high of 1300 volts when delivering full sine wave output. The
plate voltages are in antiphase so the PP volts across the OT is 2600 volts
= 920 rms.

R = V squared / W

920 x 920 / 200 = 4200

So, the primary impedance of the OT is likely to be close to 4000 ohms.

You can do the ratios for 4, 8 and 16 ohm secondaries.




......... Phil

[Joseph Meditz]

Phil Allison wrote:
"Joseph Meditz"


Would you happen to know the impedance of the OT of an Orange OR 80?

No but it wouldn't be hard to calculate.


How?


** Just using Ohm's law and a few simple approximations. The amp is push
pull so the DC voltage ( around 700 volts at idle we are told ) is applied
to the CT of the OT. The amp used 4 x KT88s ( real GEC ones) so the output,
with 700 volt supply, should be 200 watts rms or a little more.

Now, the plate voltage on each pair of KT 88s will swing from a low of about
90 volts to a high of 1300 volts when delivering full sine wave output. The
plate voltages are in antiphase so the PP volts across the OT is 2600 volts
= 920 rms.

R = V squared / W

920 x 920 / 200 = 4200

So, the primary impedance of the OT is likely to be close to 4000 ohms.

You can do the ratios for 4, 8 and 16 ohm secondaries.




........ Phil

Thanks Phill!

I just ran that for the OR 80 (80W two EL34s, Va ~ 450V) over a range
(40 to 80V) of the Vg1 = 0 curve which yielded values from about 4200
to 3400 Ohms.

I've been trying to decide on an OT for my P-P EL34 project and have
seen that 3400 Ohms appears in several examples in data sheets. But
when I plot the load line for Va ~ 420V it looks to be out of the
comfort zone for plate dissipation. I think 4300 Ohm OT from Hammond
is a safer choice.

Joe

[Phil Allison]

"Phil Allison"


** Correction to the math:

Now, the plate voltage on each pair of KT 88s will swing from a low of about
90 volts to a high of 1300 volts when delivering full sine wave output.
The
plate voltages are in antiphase so the PP volts across the OT is 2420 volts
= 855 volts rms.

R = V squared / W

855 x 855 / 200 = 3650

So, the primary impedance of the OT is likely to be close to 3600 ohms.

Sanity check:

3600 ohms plate to plate = 900 ohms per side - so when fully
conducting, one pair of KT88s will impose a 610 volts drop across 900 ohms
= 680 mA.

340 mA max per tube sounds about right with 90 volts on the plate.





........ Phil

[Eeyore]

Joseph Meditz wrote:

Phil Allison wrote:
"Joseph Meditz"


Would you happen to know the impedance of the OT of an Orange OR 80?

No but it wouldn't be hard to calculate.


How?


** Just using Ohm's law and a few simple approximations. The amp is push
pull so the DC voltage ( around 700 volts at idle we are told ) is applied
to the CT of the OT. The amp used 4 x KT88s ( real GEC ones) so the output,
with 700 volt supply, should be 200 watts rms or a little more.

Now, the plate voltage on each pair of KT 88s will swing from a low of about
90 volts to a high of 1300 volts when delivering full sine wave output. The
plate voltages are in antiphase so the PP volts across the OT is 2600 volts
= 920 rms.

R = V squared / W

920 x 920 / 200 = 4200

So, the primary impedance of the OT is likely to be close to 4000 ohms.

You can do the ratios for 4, 8 and 16 ohm secondaries.




........ Phil

Thanks Phill!

I just ran that for the OR 80 (80W two EL34s, Va ~ 450V) over a range
(40 to 80V) of the Vg1 = 0 curve which yielded values from about 4200
to 3400 Ohms.

I've been trying to decide on an OT for my P-P EL34 project and have
seen that 3400 Ohms appears in several examples in data sheets. But
when I plot the load line for Va ~ 420V it looks to be out of the
comfort zone for plate dissipation. I think 4300 Ohm OT from Hammond
is a safer choice.


That's because 80W from 2 EL34s is pushing it a bit ! I've seen them @ 70W before
but not 80.

Graham

[Phil Allison]

"Eeyore"

That's because 80W from 2 EL34s is pushing it a bit ! I've seen them @ 70W
before
but not 80.


** Never checked out any of the famous German " Dynacord " hybrid ( SS +
valve) amps from the late 60s & 1970s ?

The " Hi-Fi Favorit " or the "Eminent II " ??

Made as 2 ch instrument amps with tremolo or 4 ch PA heads.

The standard output stage was 2 x EL34s driven by 1/2 a 12AT7 "concertina"
phase splitter.

Anode volts = 750 ( ouch)

Screen volts = 450

Power out = 100 watts rms.

Power tranny = double C core,

Output tranny = multi-layer E core.

Plus lotsa NFB = THD under 1% @ 80 watts rms.

Market leader for well heeled club performers here for nearly 2 decades.





........ Phil