orange ad50 custom shop

[Orphin]

Yes, when the amp is way too cold (like about 20%) biased it will sound like pure crapsandwich.

[a.hun]

Yes, when the amp is way too cold (like about 20%) biased it will sound like pure crapsandwich.

Actually with most fixed bias amps probably below somewhere about 50% is where you'll suddenly start getting crossover distortion. It is a pretty sudden threshold, and biasing anywhere above that will sound much better than anywhere below it.

50% - 70% idling plate dissipation is about the normal acceptable bias range. Modern trend is to say 'bias to 70%', but in fact that is more a safe upper limit with most amps, NOT a target! And it may well be far too hot for many amps to run safely and reliably anyway, especially those higher voltage jobs such as big old Marshalls, Hiwatts, Oranges etc.

20% is way waaay too low. Your amp wouldn't sound like an amp at all biased to 20%. Unless it was a true pure class A job when it would actually probably sound and work just fine, just not putting out very much power.


Andy.

[Vilpur1]

Hello guys! I'm curious about what valves do you use in your AD50?

I bought my AD50 second hand about a year a go and it currently have EH 12AX7 and EL34 in it. I've got new set of Tungsol 12AX7 and JJ EL34.

[a.hun]

Hello guys! I'm curious about what valves do you use in your AD50?

I bought my AD50 second hand about a year a go and it currently have EH 12AX7 and EL34 in it. I've got new set of Tungsol 12AX7 and JJ EL34.

There isn't actually that much choice these days. EH and Tung Sol are both Russian made, JJ Slovak. The other option is Chinese brands such as Sino/Shuguang and PM. Though there are various factories and brand names in both Russia and China, and JJ in Slovakia, all of the different brands you'll see are all from just these 3 lands! What usually happens is that either amp makers or valve suppliers re-brand them, hopefully (but not always) after testing them properly.

If I had an AD50 I'd probably try to find a stock of Winged C (=C=) SED Svetlanas, excellent quality valves up 'till recently made in St. Petersburg but unfortunately no more. The amp is worth it. The other 'Svetlanas' (non SED =C=) aren't nearly as good, more run of the mill current 'New Sensor' Russian production, like 'Sovtek', 'Mullard', 'Gold Lion'. EHX seem generally a bit better to me, but tastes vary. Otherwise the JJs are a safe bet if you like their sound. Fortunately the Chinese valves are getting steadily better quality. No valves being made now are a patch on those made decades ago, but those (as NOS = new old stock) are getting rare and expensive.

My advice would be to choose which you preferred from EH and JJ and go for them again. No reason to have the same makes of preamp and power valves though. As long as the power valves are one type and reasonably well performance matched (with the amp properly re0-biased for them) you can safely pick and mix preamp valves, which also shouldn't need replaced nearly as often as the bigger power valves

Hope that helps.


Andy.

[Ade]

It's quite timely or at least a coincidence that this thread just came alive again. Two days ago I finally got around to trying out some of the extra 12AX7s I bought for my AD50. I had bought a pair of EHXs, a pair of Tungsols and a pair of the new Mullards. The stock valves I think are PMs (?).

It's a good thing I'm happy enough with the stock valves because to be honest, I could hear bugger all difference between the four sets. Admittedly I didn't record the different valves which might make slight differences more apparent. But to my ears, just swapping them out with the same settings and same two pedals, the difference was negligible. Maybe I could expect bigger difference by changing the EL34s?

Just a side note to my earlier posts. I'm using it more with my '75 PPC412 with G12H30s (see sig pic) and I'm slowly starting to bring the gain down (more around 10 o'clock now) while turning the master up.

Ade

[jontheid]

The Rocker runs two EL34's in Cathode bias with parallel 270 ohm and 330ohm resistors which gives 148.5ohms. The plate voltage is around 450v.

If your Rocker 30 has a plate voltage this high the mains selector switch may be incorrectly wired.
Usually they sit at around 340V

See this post from Ironlung40 on this thread: http://forum.orangeamps.com/viewtopic.php?f=2&t=47195" onclick="window.open(this.href);return false;

I'm a good one to ask on this. I just recently measured plates on 2 different rockers, with both demeters and mm's.

I'll let you guess which is what but here are the voltages.

1. 397V
2. 382V

Those measurements are WITHOUT tubes.

Same amp measurements with the particular tube set I used, which was different on both amps.

1. 345V
2. 336V

Now here is an interesting story. A 3rd Rocker that I tested was running 459V without tubes! I thought something was amiss. A very helpful phone interview with Will Loftin and some troubleshooting tips from him led us to the conclusion that the voltage selector switch was wired in reverse causing the higher voltage. A 4 wire swap and it brought the amp down to the same level as my example in #2 above.

I must give mad props to Will Loftin and Orange USA for being so insightful and helpful through phone conversations and email. They really went the extra mile to help me on this project. I'm a believer in their support for sure.

So, if you, or anybody has a rocker running mid 400's on the plate voltage, you should have the switch inspected, (by a qualified tech) as it may be the reason for this. But, have it checked because these amps should not run that high for any reason. I'm not suggesting that these amps have been wired incorrectly from factory on a common occurrence at all. I'm just saying that the particular one in my possession was in fact, wired wrong. Whether it was factory performed or by a subsequent owner or tech is up for debate.

[kars0747]

I recomend experimenting with 5781 in the first pre amp slot. It sounds more natural to my ears. Can´t hear the difference between 12ax7´s either, and the power tubes don´t make as much of a difference as the pre amp tubes. However, I can recommend experimenting with yellow jackets and el84´s instead of the stock el34´s. This will turn your amp into something more like a 15w amp, and this is way enough for my needs and the needs of the band. You will be able to push the power amp section harder

[Ade]

I changed the orange ecc83 preamp tube in v1 with an old stock rca 5781 with a gain factor of 70 %.

Hi

Pardon both my ignorance and reviving this old thread (there aren’t too many on the AD or Retro 50s), but what’s an RCA 5781? Is a 5781 the same as an ecc81 which is a 12at7?

I’m thinking of trying something other than a 12ax7 in V1 of my AD50

Ade

[fiveightandten]

I changed the orange ecc83 preamp tube in v1 with an old stock rca 5781 with a gain factor of 70 %.

Hi

Pardon both my ignorance and reviving this old thread (there aren’t too many on the AD or Retro 50s), but what’s an RCA 5781? Is a 5781 the same as an ecc81 which is a 12at7?

I’m thinking of trying something other than a 12ax7 in V1 of my AD50

Ade

I’ve never heard of a 5781, but the 5751 is a viable replacement. It’s inbetween a 12AX7 and a 12AT7 and has a gain factor of 70.

[Jondog]

I’ve got a 5751 kicking around. I’ve read it’s a better option than a 12AT7 for tone.

[Ade]

Thanks, 5751, that now makes sense.

Ade