#1
My amp is a jcm 900 hi gain dual reverb. I currently am using el34s, so it would be more convenient to use the same type of tube, however, if a different type of tube will work better for what I am looking for, by all means, recommend them. In my case, I am looking for tubes that are good for cleans, but still are able to handle some fairly heavy distortion. I would also like something that is able to make my cleans louder if that is possible. I play at low volumes at times as well, and need something that wont sound like crap with my amp set at 50 watts instead of 100, with the volume half way up. From what I hear hard tubes are the most durable, which makes it seem like I should go with something that will last longer.
#2
I don't think you can swap those out, unless there is a switch that allows swapping between two different tubes.

All tubes are hard, unless you know of some made from knitwear.

Good for cleans? Try Tung-Sols, Mullards, Telefunken or EHX. The preamp tube in your V1 will have the greatest impact on your tone.
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#3
A really handy quirk of the 4100 is that they actually sound quite good with el cheapo Shuguang EL34's.
Gilchrist custom
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#4
I would still have to get new tubes biased though correct? even though they are still el34s.
Also, is it acceptable to mix different pre amp tube types/brands?
#5
Mixing of brands is aye OK... A lot of people mix preamp tubes to sculpt their tones.

However, I'd recommend not mixing power tubes... its simply too much hassle. Even for powertube of the same batch of the same brand... you need to get them matched to ensure that the voltage running through each is similar.
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#6
You want a matched quad of EL34's. That's why it's good that Shuguangs sound good in them, it lessens the financial blow.
Unless you mod them, the preamp valves have less affect on the tone than you'd imagine. I have a good collection of NOS 12AX7's but I don't waste them on the JCM900. I just throw whatever into it even with mods to cut back on the SS clipping.
I'd say just chuck JJ 12AX7's in there. The last thing you need are bright/tinny Russian valves.

Edit: doing a quick bias is pretty easy on those amps. There is a single trimpot. All you need to do is adjust it until there's 39V between R26 and R27.
Armed with this schematic:
http://www.drtube.com/schematics/marshall/cd0192-iss10.gif
any tech could adjust the bias even without a bias probe. It's better to check it with a probe but you'll get away with just setting it the way I said. Don't try to do it yourself if you don't know what you are doing because you have to work on a live circuit containing hundreds of volts.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
Last edited by Cathbard at Jun 22, 2011,
#7
Thanks for the advice! I still have a few questions about my options.

Background: On the clean channel, i usually turn the pre amp to around 9' o clock and crank the clean volume knob (despite what most people say about Marshalls, I am able to get decent cleans out of it).... any gain added, i get a muddy signal, so what im looking for are tubes that let me get turn the pre amp and volume knob up, without too muddy of a signal, if that exists. I was hoping I could tweak both power and pre amp tubes to get what I want out of this amp. For the power tubes, I'm down to either JJ or EHX el34s. Which of these would fit what I'm looking for better?

As for pre amp tubes, I'll probably go with some type of JJ's, either 12ax7s or 12at7s. I know the AT7's have less gain. Would AT7's really be that bad of a choice since I'm going for cleans? Could I get just as much volume out of AT7's even though they don't have as much gain as AX7's?
#8
You have to realise something about the JCM900 Dual Reverb - it's a hybrid. It has enough valves to be an entire valve amp but there are 15 opamps and nine diodes tacked on and they do as much if not more work in the preamp than the valves do. When you turn up the gain on channel one the distortion you hear is primarily coming from four LED's clipping the signal. This happens long before you get anywhere near a valve.
If anything you want as higher gain valves as you can get your grubby little hands on. Lower gain ones like a 12AT7 would mean that even a greater proportion of any distortion is coming from SS clipping. 12AX7's everywhere is what you want. Ripping out those LED's would be high on my todo list going by what you are saying you want.

I'd take JJ over EHX and SED over both for the EL34's.
But I am serious. For some odd reason Shuguangs work very well in these jallopies.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
Last edited by Cathbard at Jun 22, 2011,