Power Attenuators Vs. Variacs

[slo100]

Re: Power Attenuators Vs. Variacs

I use a variac on my 1970 Marshall Super Bass in conjunction with a THD Hotplate. With this combo I can get awesome tone from the monster at practice volumes. It really shines up loud, however, as all tube amps do.

I have not experienced and ill-affects from use of the variac and have had no repairs stemming from its use.

I set it on 105 VAC and biased the amp accordingly. Works like a charm for me. The bad thing is if I ever want to go jam with that rig, I have to drag the variac along with me as the amp's bias would be way out of whack if I plugged it into a full 120VAC.

Amps made way back when were spec'd and designed for 110VAC. My wall puts out 122VAC. I like to think I am feeding the amp the voltage it was designed to handle as well as keeping things cool by running it a bit below.

I agree that extreme settings like 85VAC or something of the like is not good as the amp will suffer from voltage starvation.

The THD Hotplate is a great product and I'd recommend it highly. It does a good job of retaining the amps tone and it saves those poor speakers the pummeling. I have found you don't need 100 watts of power to get the volume you want but running a 100 watt power section redlined sounds damn good; even through the THD unit.

[nonamemx]

Re: Power Attenuators Vs. Variacs

Also, this JCM 800 had 4 inputs on the front. Was this possibly the modification?

[charvelguy]

Re: Power Attenuators Vs. Variacs


Did it have the inputs on the top or the front? It may be a mod but that sounds like it was one of the crossover years for the MK2.
It may look like a JCM, but it could be the std JMP. The 2150 had 4 input on top, but it was a 100watt 1x12.
875.00 for a 1x12 sounds on the high side. Depends on the mod, tolex, speaker config etc. You should try others., but if this is the one that does it for you.. then it is worth what you want to pay. Check eBay for what you might find as a 'fair' price range.

[nonamemx]

Re: Power Attenuators Vs. Variacs

It said very clearly in bold letters "JCM 800"

I dont know what you mean by top or front. The 4 jacks were arranged like so on the front, next to the knobs

00
00

The writing under the knobs (which were gold shiny chrome guitar knobs, not standard) was worn away for the most part.


It had Volume, then what seemed to be the master volume, (I had to figure these out by ear [img]/images/graemlins/laugh.gif[/img] )then Treble, Mids, Bass, and the last one was Presence (barely readible).

The "JCM 800" was plenty readible, but it had a couple of scratches through it.

IT was in good shape, it was a bit grimy, but the tolex and cloth grill seemed to be in just about perfect condition. It had a little tag in the bottom left courner of the grill that said "JCM 800".

DO you still think it could be a JMP?

[nonamemx]

Re: Power Attenuators Vs. Variacs

This is pretty close to what it looked like. I think the extra 2 jacks were added above the existing ones.

and it was only a 1x12, and this picture is a 2x12.

[charvelguy]

Re: Power Attenuators Vs. Variacs

well, if it said JCM800, them it was a JCM not a JMP, probably a modded 4410 or one of the earlier versions that may have been a crossover. I've never seen a 4 input on the front faceplate. JMP have topmount inputs like the Bluesbreaker combos. There may still be a label on the chassis, but you'd probably have to take the backing off to read it. Sounds like it is a little high in the price.
Does it have black speaker cloth or brown? Again, I'd check eBay to see what these are going for, but I'd think 5-600.00 would be more reasonable, but that's just me.

[nonamemx]

Re: Power Attenuators Vs. Variacs

[ QUOTE ]
This is pretty close to what it looked like. I think the extra 2 jacks were added above the existing ones.

and it was only a 1x12, and this picture is a 2x12.

[/ QUOTE ]

SORRY! Heres the link to the picture
http://www.rockshop.co.nz/products/gg/BotRS/jcm800.jpg

It looks just like that, but only has 1x12 and 4 bizarre input jacks.

[charvelguy]

Re: Power Attenuators Vs. Variacs

Depends on the mod I guess... they are going for around 500 on eBay. This one was a good deal with the EV.

Ebay

[nonamemx]

Re: Power Attenuators Vs. Variacs

That looks kinda like it, but its black, and has an effects loop added I guess thats what the added jacks are for on mine. (they didnt work when I plugged into one of them)

Do any of the JCM 800's have an effects loop?

The one at my store also has the large square plastic switches, not toggle switches.

[charvelguy]

Re: Power Attenuators Vs. Variacs

Sounds like a modded 4010. Some JCM800 combos came with an effects loop, but the only one I know that did from Marshall is the 4210.
You can show them the price they are going for on eBay, they may work with you or not.

[nonamemx]

Re: Power Attenuators Vs. Variacs

is that one of the ones with the diode clipping?

BTW, thanks man for the help.

[charvelguy]

Re: Power Attenuators Vs. Variacs

Not sure about your reference to diode clipping.
Marshall made alot of solid state combos, but the JCM800 combos were based on the heads of the same series,.. they were all tube,... 3 12AX7s, 2 or 4 EL34's or 6550's depending on wattage.

Did any of those pots have a push pull circuit by any chance?

[charvelguy]

Re: Power Attenuators Vs. Variacs

[ QUOTE ]
I use a variac on my 1970 Marshall Super Bass in conjunction with a THD Hotplate. With this combo I can get awesome tone from the monster at practice volumes. It really shines up loud, however, as all tube amps do.

I have not experienced and ill-affects from use of the variac and have had no repairs stemming from its use.

I set it on 105 VAC and biased the amp accordingly. Works like a charm for me. The bad thing is if I ever want to go jam with that rig, I have to drag the variac along with me as the amp's bias would be way out of whack if I plugged it into a full 120VAC.

Amps made way back when were spec'd and designed for 110VAC. My wall puts out 122VAC. I like to think I am feeding the amp the voltage it was designed to handle as well as keeping things cool by running it a bit below.

I agree that extreme settings like 85VAC or something of the like is not good as the amp will suffer from voltage starvation.

The THD Hotplate is a great product and I'd recommend it highly. It does a good job of retaining the amps tone and it saves those poor speakers the pummeling. I have found you don't need 100 watts of power to get the volume you want but running a 100 watt power section redlined sounds damn good; even through the THD unit.

[/ QUOTE ]

'sound' advice [img]/images/graemlins/grin.gif[/img]

I do the same with my old Marshalls.. just slightly running the voltage under 110V with a Variac. I haven't tried the got plate, as as have the SE100..but I think I will.

[Twisteramps]

Re: Power Attenuators Vs. Variacs

If it's a channel switching Marshall JCM800, it has diode clipping. Not sure if this is the case, I'm coming into the thread late. [img]/images/graemlins/smile.gif[/img]

Pete

[ QUOTE ]
Not sure about your reference to diode clipping.
Marshall made alot of solid state combos, but the JCM800 combos were based on the heads of the same series,.. they were all tube,... 3 12AX7s, 2 or 4 EL34's or 6550's depending on wattage.

Did any of those pots have a push pull circuit by any chance?

[/ QUOTE ]

[charvelguy]

Re: Power Attenuators Vs. Variacs

then the 4210, the 4211,and the 4212 have diode clipping as they were based upon the 2205 and the 2210 which were channel switching JCM800's.
I still think it is a 4010...but at this point it is just speculation.