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Post subject: THD Hot Plate
Posted: Fri Aug 10, 2007 1:15 pm
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Anybody knows if a THD 8ohm hot plate works on a Hot Rod Deville 212


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Post subject: switch on thd for ohm setting
Posted: Fri Nov 16, 2007 9:16 am
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hi i actually called mf and asked them which thd hot plate to buy as i have the 2x12 deville as well,, nobody answered me i was like wtf,, then i read somewhere that the thd has a switchable ohms button on it the unit itself so i beleive the answer is yes and what are the ohms on our deville;s/? i forget but its like 2- 4-8 i think i have to go look now ok just looked in manual it says 4 or 2 ohms so if you get thd hot plate put it on 4,, i am gonna get 1 as well soon,, check what i am telling you because i am just learning about this myself hope it helps rock on Dave----pS i just read the only channel that is actually tube on these devilles is the clean channel the drive channels are solid state-------i was like what?/ kinda surprised read this on here,, in another room posted question in modern amps to see if its true------later


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Post subject: Re: THD Hot Plate
Posted: Tue Nov 20, 2007 11:42 am
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RickoMas wrote:
Anybody knows if a THD 8ohm hot plate works on a Hot Rod Deville 212


the deville 212 is a 4 ohm speaker cabinet: 2x 8 ohm speakers in parallel

you need to get the 4 ohm hotplate for this amp.

the 410 deville is 2 ohms (like the original bassman): 4x 8ohm speakers in parallel


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Post subject: 299
Posted: Tue Nov 20, 2007 2:14 pm
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your not gonna beleive this,, i went today hell bent on gettin the 4 ohm hot plate for my Deville,, i went to 2 places and they were like nope!!! don; t have that so i came home 300 richer but still have the void looks like tommorow i will call musicians friend i guess,, [sorry about that last post of mine} learning ya know--- DO NOT TAKE MY ADVICE JUST DANGEROUS ENOUGH TO BLOW EQUIPMENT UP hehehehee rock on dave :P


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Post subject:
Posted: Tue Nov 20, 2007 2:31 pm
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yeah, that's the only problem with the THD, the come in a single impedance per unit, and are not switchable (which might be a good thing, prevents damage if it were switched while in use).

Also, each version is a different color: gold, blue, purple, red, green, etc....

I believe they came in the following versions:

16 ohm, 8 ohm, 4 ohm, 2.7 ohm, 2 ohm

the 2.7 ohm is for an amp with 3 8-ohm speakers, such as the Fender VibroKing (Clapton used this amp in the late 90's early 2000's)

inverse ( 1/8 + 1/8 + 1/8 = 3/8 = 1/2.7 ) = 2.7 ohms

so... for speaker (impedance) loads in parallel (like a full marshall stack):

take the inverse of the impedances, add em, then invert that final number

1/x1 + 1/x2 + 1/x3 ... 1/xn = n/xtotal (where n = number of speakers)
inverse of n/xtotal = xtotal/n

overall impedance = xtotal divided by n

For speaker impedances in series (you rarely see this):

just add the impedances

16 ohms + 16 ohms = 32 ohms
8 ohms + 8 ohms = 16 ohms
4 ohms + 4 ohms = 8 ohms
2 ohms + 2 ohms = 4 ohms

16 + 8 = 24 ohms
8 + 4 = 12 ohms
4 + 2 = 6 ohms


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Post subject: Re: THD Hot Plate
Posted: Mon Nov 26, 2007 2:36 pm
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dta74 wrote:
RickoMas wrote:
Anybody knows if a THD 8ohm hot plate works on a Hot Rod Deville 212


the deville 212 is a 4 ohm speaker cabinet: 2x 8 ohm speakers in parallel

you need to get the 4 ohm hotplate for this amp.

the 410 deville is 2 ohms (like the original bassman): 4x 8ohm speakers in parallel


This is half right. THe 212 is 4 Ohms (2 8Ohms in parallel) but the 410 is 8 Ohms, NOT 2 Ohms. This is achieved by wiring the speakers in 2 sets of parrallel (which makes 4 Ohms) then wiring the 2 sets in series, which raises the impedence to 8 Ohms.

If you take a 2 Ohm Hot Plate to the DeVille 410, bad things will likely happen - you need the 8 OHm.

With regards to the 8Ohm to the 212, you could probably get away with it, since the Hot Plate is greater than the amp. However, (1) you will NOT achieve the ultimate efficiency of the amp since the two impedence are miss-matched, and (2) you will need to hook an 8 Ohm cabinent to the Hot Plate. Since the 212 cab is rated at 4 Ohm, you won't be able to use it.


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Post subject:
Posted: Tue Nov 27, 2007 10:51 am
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Sorry, I was thinking about the Bassman which is a 2 ohm load. However, looking at the schematics for the blues deville 212, there is a 2 ohm tap on the transformer and the 212 is actually rated for a 2 ohm load with an external speaker cabinet.

Regardless, make sure your speaker load is MATCHED or HIGHER than the output of the transformer. Just think of it as trying to do 55mph in 2nd gear... you'll get there, but at you'd be running the engine at redline. Likewise, running an 8 ohm speaker into a 4 ohm amp is like trying to do 30 mph in 4th gear... the engine will bog down and not produce full power. Its a similar concept with a tube amp.

Also, note that this is NOT the same for Pro Audio amplifiers... they are rated for a given output at a certain speaker impedance and will auto switch their internal impedance settings based on the speaker load that is plugged in.

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