# Garnet amps, ok with a 16 ohm load?



## bolero (Oct 11, 2006)

hey I have a Garnet Jammer 1x12 combo & I want to use a 16ohm speaker in there, think there'll be any issues?

I'll have a look at the OT wires to see if there's an unused tap, but I think they're all 8 ohm stock?


thx!!


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## Ripper (Jul 1, 2006)

bolero said:


> hey I have a Garnet Jammer 1x12 combo & I want to use a 16ohm speaker in there, think there'll be any issues?
> 
> I'll have a look at the OT wires to see if there's an unused tap, but I think they're all 8 ohm stock?
> 
> ...


Garnet amps are usually 8 and 4 ohms.


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## bolero (Oct 11, 2006)

do you think mismatching with a 16ohm would be a bad idea?

assuming it's the 8ohm tap that's hooked up, not the 4 ohm


thx!


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## parkhead (Aug 14, 2009)

Kevin Oconnor says with a properly designed output transformer Impedance selection should be selected like a tone control...


p


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## greco (Jul 15, 2007)

parkhead said:


> Kevin Oconnor says with a properly designed output transformer Impedance selection should be selected like a tone control...
> 
> 
> p


This is interesting...not that I fully understand EXACTLY what he means.
Hope others see this and comment.

Bolero...this question comes up often. If you have a impedance mismatch with a tubes amp, *it is my understanding *that 100% mismatch (i.e, 4 ohms to 8 ohms or 8 ohms to 16 ohms) *is OK if you are not playing at loud volumes for extended periods of time. * You apparently risk shortening the life of your tubes. 

Cheers

Dave


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## parkhead (Aug 14, 2009)

When a designer builds and amp he goes to the catalog of off the shelf transformers and selects one that is close to what he needs. 

The output tubes have a range of impedance that they'ed like to see 
so he chooses the transformer that can handle the wattage at the right price point and builds his amp 

impedence is actually about turns ratios so the same transformer might have two applications, for example the Twin 2k primary 4 ohm secondary 
will also work as a 4 k primary 8 ohm secondary 

If the designer wants a more hi fi or linear sound he shoots for a higher primary impedance. If he wants to max out the power at the expense of bandwith he lowers the primary impedance. 

If you look at Jtm45's they were off the shelf hi fi multipurpose outputs 6k6 primary to a multi-tap secondary. 
After 66 Marshall had transformers built to their specs and dropped the primary to 3400 to increase the power output and get more distortion harmonics. 

they probably arrived at this change in spec by experimenting with impedance settings. 

leo fender used the same output transformer for the tweed bassman and 3 10 bandmaster, likewise the 3 10 vibro king uses the reissue bassman OT. 

the bassman specs are 4k primary to 2 ohm secondary 
the bandmaster specs are 5 or 6 k primary to 3.2 k secondary 
its the same transformer and taps, the secondary impedance determines the primary via the turns ratio 

The key thing you need to ask is Can the primary wire handle the full wattage of the amp ... 
If it can you can probably mismatch 100% down and 100% up 

if it can't you are probably better off mismatching up 100% using a 16 ohm speaker with the 8 ohm tap. This raises the primary impedance the tubes see and makes the amp more linear.

Running a Head without a speaker destroys the output transformer because the primary charges up but the secondary has no load ... the charge in the primary has to go somewhere & it discharges by arcing, burning the transformer. 

Output tubes are self limiting, if an amp uses 2 6v6's and makes 20 watts at an 8 ohm load, 2 6v6s can't make 40 watts into a two ohm load, their bias 
limits them to 20 watts. If on the other hand the amp is designed improperly 
using a 10 watt output transformer for a 20 watt pair of 6v6's (the tweed deluxe) the transformer will fail at some point ...
probably when the old jensen blows up & the player is wailing away on the amp asking "did I just lose sound? strum strum POP!" Very few tweed deluxe have their original output transformer, or speaker for that matter. They sound just too darn good wound out. 

I believe it was kendrick amps that labeled their impedance selector TONE. 

Kevin O'connor writes about this stuff in his excellent book TUT (The Ultimate Tone) as much as I respect Kevin and his engineering expertise, and pour over his book regularly, some of his concepts, like using diodes to create distortion in tube amps are engineering instead of tone solutions. 

I've used this impedance matching & mismatching to solve problems. I have a 62 princeton that sounds killer & its been my main amp for years livingroom & small gigs. It was hacked long ago for a 12 inch speaker instead of a 10. So it runs a vox blue. When i was gigging it regularly I ordered a reissue deluxe OT from fender, same mounting holes, lower 6k primary impedance and physically larger core. I carefully packed away my original OT and run the deluxe OT. For medium gigs I also run an extension cab. My amp is slightly louder because of the lower primary and is 100% safe with being stressed since its a 20 watt OT replacing a 12 watt unit & the amp is 12 watts on a good day. 

If I were doing it again I'd order an aftermarket deluxe OT with a 16 ohm tap, hook up the 16 ohm tap to the 8 ohm jack and get a 3 or 4k primary, and a little more marshall style grind. 

Hope this explains stuff. 

keep in mind if your model amp is Famous for Blown output transformers stick with matching impedances. Further if your plan is to run your amp on 10 at all times stick with a matched setup as there are added stresses when you are forcing the output to conduct a square wave (dc) on a continuos basis. 
This is why old attenuators blew up outputs. 

If your intention is to run your amp on 10 at all times, look at replacement transformers that might help you out. Any 2 6l6 fender amp with an 8 ohm load can Run the Twin output transformer, get huge bottom end and never stress it. I once ran a Twin OT in a deluxe, the sound was total SRV in a small package the bottom end was HUGE and tight. 

I have a sunn head with a replacement power transformer, it's setup to run 2 6v6's, its probably 15 watts, but its the biggest 15 watts you've ever heard because of the Huge 100 watt output transformer the amp has. 

p


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## bolero (Oct 11, 2006)

wow, great stuff, thx Parkhead :rockon2: :rockon2:

funny enough I just got an old Garnet 2x12 cab with 16 ohm impedence stamped on the model ID tag on the back...interesting, some of those Garnets must have a 16 ohm tap on the OT?

100w OT in a 20 watt amp, funky...

conversely: I wonder if you could sufficiently isolate the prim/secondary windings of a 20w OT so it's *impossible* for them to short out....then crank that into a 100w amplifier...could you get a massive amount of tortured OT sound we all love, with no threat to the amp/tubes?


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## parkhead (Aug 14, 2009)

bolero said:


> wow, great stuff, thx Parkhead :rockon2: :rockon2:
> 
> funny enough I just got an old Garnet 2x12 cab with 16 ohm impedence stamped on the model ID tag on the back...interesting, some of those Garnets must have a 16 ohm tap on the OT?
> 
> ...


well you could always fuse the power transformer, buy a $20 20 watt OT 
and have a fire extinguisher handy 


p


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