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Silvertone 1485 - 8 ohms?
Silvertone 1485 - 8 ohms?
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Old 27th December 2017, 08:11 PM   #1
rave0035 is offline rave0035  United States
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Default Silvertone 1485 - 8 ohms?

Hi all - I'm rehabbing a Silvertone 1485 amp for a friend. Schematic is here.

This amp is horrific to work on. The circuit is very strange, and everything is buried in a rat's nest... the chassis is long, skinny and deep. I digress...

If you're familiar with this amp, you'll know that the original cab presented 2 separate 2.66ohm loads to this head. For obvious reasons, that's not practical.

This particular unit has one original OPT and one Mojotone replacement.

The Mojo unit has 4ohm and 8ohm taps on the secondary. The original uses the same color coding, and has an unused (presumably 8ohm) tap, just like the mojo.

My questions are this:
1) Does anyone know if the Mojo replacement is identical to the original?
2) If that's the case, is there any reason I can't just switch to the 8ohm taps and live happily ever after?

Mike
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Old 29th December 2017, 03:16 AM   #2
PRR is online now PRR  United States
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Mojotone makes many transformers. Does this one have a number? Is it on Mojotone's site?
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Old 29th December 2017, 12:18 PM   #3
rave0035 is offline rave0035  United States
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Yes and yes!

SKU # MOJO1485

Silvertone 1484 1485 Output Transformer
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Old 30th December 2017, 12:09 AM   #4
PRR is online now PRR  United States
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Are you keeping the six-cone cab? Or do you only have the head?

This IS a wacky amp. Aside from the odd three-fer speakers, there's two OTs. (Not to mention the PT...) Obviously they could not get OTs over 60W nor speakers over 20W (at the price they wanted).

Today, head-only, I guess I would take two 8 Ohm taps to two jacks.

It is tempting to parallel the "8 Ohm" taps to one "4 Ohm" jack. However we don't know how close the ratios are, stock and clone. Nothing horrible will happen (if output is way-low, reverse one primary). If ratios are a little off, clean and max power will be slightly down. But if raw power is the main goal, get a Fender or other mainstream monster.

I believe Mojotone support is somewhat helpful.
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Old 30th December 2017, 01:17 AM   #5
rave0035 is offline rave0035  United States
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Don't have the cab, which is why I'd like to run this at 8ohms rather than building a 6 speaker monstrosity. I can live with two jacks on this thing if I have to.

Assuming the OTs are identical, is it safe to hook up the 8ohm secondaries without ruining anything upstream?

You're correct - this amp has 'as cheap as we can' written all over it.

I'll get in touch with MT and report back.

Thanks PRR!
Mike
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Old 31st December 2017, 05:40 AM   #6
PRR is online now PRR  United States
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Put one 8r load on each transformer; or parallel the two 8r windings to one 4r jack and 4r load (less confusing).

Try the 4r trick with very soft signal. If the transformers are not in-phase (color-codes got mixed; more likely at Silvertone than MT) then the 4r connection will work with one winding but two will short each other and be very weak. Reverse one OT's primary plate wires, it will be right. Don't play LOUD until this is sorted: an un-loaded OT played LOUD may arc internally.
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