High Gain Orange Amps

[Smokebreak]

The cathodyne trick is adding a large grid stopper at the cathodyne grid. 1M works and smooths things out.
Also check Weber's 6o100 schematic for ideas/extras . Iirc a mid pot, presence,etc. https://taweber.powweb.com/store/6o100_schem.jpg

[gingertube]

The cathodyne has trouble when the loads on the anode and cathode become unbalanced.
This happens on signal peaks when the output tubes start drawing grid current.
The most important thing for a higher gain amp with a cathodyne is to push up the value of the output tube gridstops. Try 47K. This limits grid current into the output tubes and thus limits the un-balancing of the cathodyne.
Watch that you still meet the max Rg1 values when you push up the gridstop value.

You can then also address the overload of the cathodyne itself, that is what the large gridstop resistor on the cathodyne is about. This is less important since the cathodyne should not go into overload untill well after the output tubes.

I prefer the AC coupled cathodyne. It's operating point is then NOT at the mercy of the preceding gain stage but seeks it own operating point.

The Merlin link :
http://www.valvewizard.co.uk/cathodyne.html

Cheers,
Ian

P.S. A copy from a post I did to another forum on this topic:

Calculating Overdrive Effects
If MATHS gets on your wick then skip to the SUMMARY below:

For equal loads on Anode and cathode on the Cathodyne

Zout = RL.ra/RL(u+2)+ra

The ra term on the bottom line is insignificant compared to RL(u+2) term so drop it. Then the RL terms top and bottom lines cancel leaving

Zout approx = ra/u+2

At typical values of u (>=20) u+2 approx = u, so simplify again

Zout approx = ra/u = 1/gm

So for equal loads at the anode and cathode the Zout at both is approximately 1/gm or about 650 Ohms for a 12AX7

If driving output stage directly The equal loads on Anode and Cathode will NOT be guaranteed if Output Stage strays into grid current (trying to overdrive the output tube). When this happend the load resistance presented by the output tube grid drops significantly.


If the Anode load drops significantly then:

Zout cathode = RL+ra/(u+2) x ra/RL The ra/RL term insignigicant so

Zout cathode approx = RL+ra/u+2 At usual values of u

Zout cathode approx = RL/u + ra/u = RL/u + 1/gm

That is it increases by RL/u


If the cathode load drops significantly then:

Zout anode = RLxRL(u+1)+RL.ra / RL(u+2)+ra

RL squared (u+1) is much larger than RL.ra and RL(u+2) is much larger than ra so

Zout anode approx = RLxRL(u+1)/RL(u+2)

and at reasonable values of u

Zout anode approx = RL


SKIP TO HERE:
SUMMARY:
As the loads on Anode and cathode become unbalanced (as when overdriving the output tubes) then

Zout anode increases from 1/gm toward RL (from 650 Ohms toward 100 KOhms in the Orange)
Zout cathode increase from 1/gm by maximum factor of RL/u (from 650 Ohms toward 650 + 100K/100 = 1650 Ohms in the Orange)

The imbalance from an over driven output will therefore be worse with the 100K resistors like in teh Orange compared to say a Fender 5E3 with 56K resistors but the difference between the anode and cathode output impedance in overdrive is so dramatic it doesn't really matter if its between 650 Ohms and 100K or between 650 ohms and 56K, Also the effect of this will be asymetrical, affecting one side of the push pull and therefore introducing large gobs of 2nd harmonic distortion.

The trick here is to use large grid stops on the output tubes to reduce the loading effects on the cathodyne. Take those output tube grid stop resistors way up to say 47K. THis is effectively tuning the amount of 2nd harmonic distortion you get in overdrive.

[dcribbs1412]

Thanks rp
I contacted the link and Nathan replied he "can supply everything you need to build the complete Amp up".
Which is great news. I'm trying to keep cost down and use on hand stuff.
But realize the PT I have (was going to use for a lower voltage 2204 build)
570V,285-0-285 may not be up for the task. Seeing info of 470-500 plate voltages on a lot of the Orange amps. Not sure if I should give it a go
or get some bigger iron.

D

[M Fowler]

I'm going to put together a Weber Orange 100w amp kit and changed it over for bass guitar for my brother-in-law. Orange tolex and white face plate. He will really like that.

Have fun with your project Darin.

[dcribbs1412]

I'm going to put together a Weber Orange 100w amp kit and changed it over for bass guitar for my brother-in-law. Orange tolex and white face plate. He will really like that.

Have fun with your project Darin.

Nice Mark
Brother in law's gotta love that

D

[gldtp99]

Vid of a 74-ish OR80 clone I built several yrs ago----- the player who bought it did this vid a couple of weeks ago.
Amp is sitting on top of the Mesa 4x12.
I used a Twin Reverb replacement PT and an Edcor 100 watt, 4.2k primary OT, Mercury 10H choke.

Vid:

https://www.youtube.com/watch?v=xzb04NnZ46o

[jazbo8]

Orange tolex and white face plate. He will really like that.

Where are you ordering the tolex and the face plate (with graphic or no)?

[rp]

I'm trying to keep cost down and use on hand stuff.
But realize the PT I have (was going to use for a lower voltage 2204 build)
570V,285-0-285 may not be up for the task. Seeing info of 470-500 plate voltages on a lot of the Orange amps. Not sure if I should give it a go
or get some bigger iron. D

Think a proper clone will be expensive, at least with the Heyboer iron. Nice thing about the Orange is they used Celestions so it shouldn't be so hard to capture the original sound, compared to something like Hiwatt where those original ported cabs w/ Fanes were half the sound.

Check the schematics IIRC Oranges used a voltage doubler, but you can always just change that. ~500V on the plates is a part of the sound, I hear it anyway, there's some of that ~500V era Marshall bite in there.

Here's an other one for you:
https://www.youtube.com/watch?v=EK89EVPRaX4

[dcribbs1412]

Vid of a 74-ish OR80 clone I built several yrs ago----- the player who bought it did this vid a couple of weeks ago.
Amp is sitting on top of the Mesa 4x12.
I used a Twin Reverb replacement PT and an Edcor 100 watt, 4.2k primary OT, Mercury 10H choke.

Vid:

https://www.youtube.com/watch?v=xzb04NnZ46o

Nice clip gldtp99
was hoping you would chime in, your Mule 80 clips sound really nice
you tweaked the tone stack?
Thanks rp
grew up listening to my brothers listening to free and Bad Co.
Orange must have been the "house" amp for that studio.

D

[M Fowler]

Orange tolex and white face plate. He will really like that.

Where are you ordering the tolex and the face plate (with graphic or no)?

I'm just using the complete head kit from Weber instead of putting together an exact looking Orange clone. The Weber kit is Marshall large box looking cabinet and Weber faceplate options.

I had thought about making my own chassis with large Orange style front panel but ditched that idea, too much monkeying around to make it worth while. Also, I had looked at that Facebook guy's kits but decided against that too.

Mark

[gldtp99]

Thanks--- I took my 1974 Orange OR80 to my shop today for a check over and to fire it up---- it had been sitting in storage for a while.
I installed the stock 330pF bright cap on the Vol pot----- I didn't put a bright cap in this one when I replaced the Vol pot as part of the initial service, yrs ago.
I like the breakup tones better with the bright cap installed, I found out.
One of my amp customers was over and he played the amp for a while and liked it----- he'd never played a Vintage Orange before.
I think it might be time to build another circuit clone----- I've got spare Hiwatt sized blank chassis and a Hiwatt type bare wood head cab on hand--- I just need to find a rotary switch for the FAC control and a faceplate----I have a custom wound Heyboer Twin Reverb/Showman 4/8/16 ohm OT with a 4k primary----- for PT's I have a Twin Reverb/Showman Classic Tone and some custom wound massive capacity Heyboers (330-0-330 at 600mA and 10A heaters).
I also have the Orange 140 replacement PT (Drake) from the set I bought to get the OT and choke for my OR80 yrs ago.
Massive iron and very high B+ seems to be the trick for vintage Oranges----- I might not go for the orig B+ levels but instead @450-475V level of the Twin Reverb PT.
Today's output tubes will work longer at the lower B+------ the clone in the vid has proved to be a reliable workhorse for the owner----- I'd sacrifice a bit of ultimate Vintage Orange tone for a more reliable build.............. gldtp99

[dcribbs1412]

gldtp99
Thanks for the info
hope you document a build if you decide to build another clone
rotary switch for FAC is MBB or BBM make before break or break before make, or does it matter?

https://www.tubesandmore.com/products/P-H392
https://www.tubesandmore.com/products/P-H393
also wondering if the small coil (2mH i think) used in older models presence/boost circuit makes a difference?
So the clones in your clips have lower voltages than original?
any experience with using 47k grids like gingertube suggests?
appreciate your time

D

[gldtp99]

gldtp99
Thanks for the info
hope you document a build if you decide to build another clone
rotary switch for FAC is MBB or BBM make before break or break before make, or does it matter?

https://www.tubesandmore.com/products/P-H392
https://www.tubesandmore.com/products/P-H393
also wondering if the small coil (2mH i think) used in older models presence/boost circuit makes a difference?
So the clones in your clips have lower voltages than original?
any experience with using 47k grids like gingertube suggests?
appreciate your time

D

Thanks for the links to the rotary switches but I'm sure I have some in my parts stash.
In the OR80 clone in the vid I used a rotary switch pulled from one of the many old PA heads I have in my shop or storage---- I'm sure I have another----I'm not sure if it's a break before make or not.
On my real 1974 Orange OR80 the FAC switch will produce a loud "Thump" if the FAC control is turned counterclockwise (making the amp bassier) with the amp volume at playing level----- would that be a break before make switch or a make before break switch ?
I've never dealt with the circuits that use the small inductor in the NFB/Presence/HF Boost circuit---- my real '74 doesn't have the mini coil and I set out to use that circuit to copy, so I've never considered trying to find a suitable small inductor to build a part of a circuit that I've never been interested in building.
Also I haven't had problems with the cathodyne PI---- I just built the same circuit as my '74.
The other day when I added the 330pF bright cap to my '74 and tested it out, I cranked it progressively up to full volume to see if the amp was operating properly----- all it did was put out glorious vintage distortion.
I'm not really any kind of expert on Orange amps----- I have a 1974 OR80 that I rescued from being a basket case and I've built one amp based on that circuit----- the one in the vid.
I have serviced up another 1974 OR80 that was eating output tubes and serviced up an inop 120 Slave (bad pot, dirty jacks, cap job) but that's as far as my Orange experience goes.
I wasn't trying to re-engineer the circuit (or re-invent the wheel) with the one clone I built----- I used the oversized (for an 80 watter) iron I had on hand---- the Twin Reverb replacement PT puts out @450V B+ and since I had the particular PT, and that B+ would be easier on today's EL34's...... I used it.
That one clone I've built has found an owner who loves it and it's been reliable for several years of rehearsals and shows for him----- and I believe that it's still running the same set of Shuguang EL34B's (Valve Art branded) that I initially put in it.
I was just thinking that I could build up another somewhat similar amp using parts that I have on hand now.
The iron in my real '74 OR80 is just massive----- the same iron as an OR120---- so the current capacity of the PT is way more than an EL34 x 2 amp could use under these conditions, the B+ is @515V------ the OT is equally massive, being rated to handle EL34 x 4.
So I'm going to use the iron I have on hand that most closely approximates the iron in my '74----- except I'd rather have @450V B+ for output tube reliability instead of the 510-520V B+ that I've actually measured in the vintage Oranges that have crossed my bench................... gldtp99

[Blindog]

Double

[Blindog]

FYI http://hilbishdesign.bigcartel.com/

Can't personally say if this site is a good and reliable provider or not. Someone here was working on a clone with parts from the above link but the post died out and I don't recall who.

Word is that Heyboer winds a fine set of Hiwatt Partridge clones. Now the question is if the Orange and Hiwatt trannies were off-the-shelf or proprietary winds? Hopefully, someone here knows and can chime in, I myself would love to know, and moreover I've always wondered if the Hiwatt, Sound City, and Orange iron was all the same? Even if different the Heyboer Hiwatt iron is likely your best bet.

There's an Orange database website out there too with pictures and info.

I wouldn't bother building a modern Orange clone when the old ones are so cool, and you can prolly pick up a used modern amp off Craigslist for what it would cost you to build it.

That was me! Here's a link to my build thread.

https://tubeamparchive.com/viewtopic.ph ... 349#336349

Nathan is great to work with, no worries!

Here's some inspiration for my build:

https://www.youtube.com/watch?v=NH5wbYP5xkQ


Mark