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Fattening up an AD200b

C

CircleOfCrows

Mar 28, 2013
187
34
Australia
#1
Hi Guys
I have a stock standard Orange AD200b-factory tubes.
I am finding it lacking particularly as I push the gain past 12(o'clock)- It thins out and loses bottom and definition.
Am considering swapping the power section to kt88's plus is it worth changing to lower gain preamp valves (at7's/ au7's?)

Are there any Mods commonly done to this amp? About the only thing I have really read about is changing the Iron to a Mercury Magnetics transformer (for mixed review of improvement).

I am happy with the amount of power it has Just wanting to keep it balls and bottom heavy throughout its range more.

Any help,experience or suggestions appreciated.

C.
 
#2
Main limitations on it are the output transformer and the later stages of the circuit, not enough drive to push the KT88 to their full potential. Basically, instead of rebuilding the whole amp, might as well get a better amp, suited to do stuff other than saggy overdrive. Maybe check its working right to start with though, valves tested and such.
 
#4
Hi.

+1 on the OT acting as a HPF when the power goes up.

Unless of course the bottom loses definition regardless of the master volume, then the problem/feature lies in the pre section.

When was the last time the amp was serviced?


The easiest and cheapest way to try improve or change tube amps tone is pre amp tube rolling, so I'd try that first.

Regards
Sam
 
#5
Hi Guys
I brought it brand new. Hasn't been serviced. Haven't had it that long either-maybe 3 months max, used once a week at band practice only. No noticable faults. I realise orange just use what ever tubes they can get there hands on at the time(of a reasonable quality/price). I AM HAPPY to try different tubes but don't know what I should be trying-

Mr.Foxen would you advise against kt88's in this amp?

It sounds good if I am pushing the master and using the gain as a volume control per se. Works great If I am using a pedal to slam the front end this way as well/for drive. Until about 12 on the gain it maintains enough bottom- from that point it gets angrier and the bottom drops off/it gets lost in the mix. If it maintained bottom all the way through I would be happy with it.

The general character of the amp is fine for me. I am familiar with tube amps and it has more than enough volume for my purposes. I am open to changing things on the amp if it will get me to where I want it to be.

Any suggestions on what I should be changing in the pre?
I have an authorised tech I know and trust I will be getting to do anything needed- simply looking at options

C.
 
#6
CircleOfCrows said:
Hi Guys
Mr.Foxen would you advise against kt88's in this amp?
Click to expand...

Pretty sure its designed for KT88, its the amp I'd advise against, design priority 2 after being KT88 is being cheap to make. Thing is, if it has 6550 at the moment, chances are cheap KT88 and 6550 are basically the same thing in different shaped bottles. Its not the valves that are the limiting factor, its the transformer and the circuit.
 
#8
The AD200b is designed with 6550s, though as Foxen says, they're practically the same when buying lower end. When I bought mine used, it was equipped with a quad of Winged C 6550s and it roared through my OBC115. I had a tube become microphonic a few months later (and the set was close to being on their last leg), so I replaced them with some JJs (also 6550s). I noticed a slight difference in beef (or lack thereof) with the JJs - those happened to crap out right away (faulty from the factory), so my amp was back to the shop. I'm now in the process of fitting them with Winged Cs again, so we'll see how that goes.

As mentioned above - cab is definitely another factor in the equation.
 
#10
P-oddz said:
The AD200b is designed with 6550s, though as Foxen says, they're practically the same when buying lower end.
Click to expand...

Don't assume because they ship with 6550 currently that they were designed for them. Its derived from a Matamp design, and being British, it would be KT88 as that's what were used in the UK, 6550 being US valves. They used to be shipped with KT88, but 6550 seem to have turned out cheaper.
 
#11
Mr. Foxen said:
Don't assume because they ship with 6550 currently that they were designed for them. Its derived from a Matamp design, and being British, it would be KT88 as that's what were used in the UK, 6550 being US valves. They used to be shipped with KT88, but 6550 seem to have turned out cheaper.
Click to expand...

+1 Originally The Marshall JTM45 was equipped with the KT66. 6L6GCs would work quite nicely in them. I still have a pair of the KT66s that came out of my amp.
 
#12
Mr. Foxen said:
Don't assume because they ship with 6550 currently that they were designed for them. Its derived from a Matamp design, and being British, it would be KT88 as that's what were used in the UK, 6550 being US valves. They used to be shipped with KT88, but 6550 seem to have turned out cheaper.
Click to expand...

Actually the AD200 is based on the preamp of the AD30 guitar amp with a differently tuned tone stack, which in turn has more in common with the Vox AC30 than anything out of Matamp. I own one of the first AD200B MkIII's and it came with Winged C 6550C's. The MkI and MkII models had smaller chassis' similar to the AD140 and could not physically fit KT88s at all, only straight bottle 6550s like the Winged C. So no, it's British heritage does not mean it was designed for the KT88 explicitly.

To the OP- get some better preamp tubes to roll in and think about using something with lower gain like a 5751 or 12AT7 in V1 or V2. That will get you more control over the gain since it will have more variance within that nice zone where the drive is compressing slightly and only overdriving when really digging in or slamming some double-stops.
 
#15
I think most players' issues with the AD200's volume is they're not used to turning up their amp's master as much. My understanding is the Orange's use double-logarithmic pots on Master and Gain so with the gain below 2 or 4, depending on your tubes, you can push the master to full and still be clean. Way different than an Ampeg that starts breaking up at 4 or 5 on the Master even with the gain low.
 
#16
chadds said:
Tube rolling is somewhat effective yet it is the nature of the beast that as amps run out of headroom you lose that big bass. 100 watt amps do it sooner. A Marshall Superbass or Superlead 100 have nice tube fidelity until you crank them. Kinda would suggest loving that amp and not cranking it past your tone goals.
Click to expand...

Massively depends on the output transformer, I have 100w amp that has huge low end, but it has transformers nearly as big as SVT ones. Marshall tend to go little on transformers, except the 2001, that had serious iron.
 
#18
I am familiar with tube amps and it has more than enough volume for my purposes.
KIh4wb
 
#19
Hi.

CircleOfCrows said:
Hi Guys
I brought it brand new. Hasn't been serviced. Haven't had it that long either-maybe 3 months max, used once a week at band practice only.
Click to expand...

Have Your tech bench it then, there may be a weak tube or two in there.

CircleOfCrows said:
I AM HAPPY to try different tubes but don't know what I should be trying-

Any suggestions on what I should be changing in the pre?
I have an authorised tech I know and trust I will be getting to do anything needed- simply looking at options
Click to expand...

I'd start with the same types of better/known quality.

That's what I did with my Fame (Smarvo).

The pre tubes are from $5 to $20 and You'll need spares anyway.

CircleOfCrows said:
-cab has nothing to do with it. I am using an OBC115-
Click to expand...

:)

IOW, a TL606.

They are known to be a bit deep bass shy when loud volumes are the requirement.
At least mine have been that way.
TL505's are marginally better, more so as a pair ;).

Regards
Sam
 
#20
I think the low end is not actually being rolled off as the gain potentiometer is adjusted upwards. It only sounds that way as the distortion/harmonics increase emphasizes the mid range. Perhaps that design philosophy means you have to adjust the EQ to reduce the mids and boost the bottom as the gain is increased. Due to the way human frequency perception works (look up Fletcher-Munson), the mids will sound much more prominent as volume goes up, until it gets really loud, then the bass frequencies seems to take over.
 

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