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Post subject: Fender Bassman 59 Reissue LTD and Attenuator/Load Boxes
Posted: Sun Nov 24, 2019 12:38 pm
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Is it possible to tap ONE of the FOUR speaker level outputs of a 'Fender Bassman 59 Reissue LTC' to be able to connect said single speaker output via a male RCA to 1/4" male speaker cable, then connect the 1/4" male to an attenuator/load box, i.e.: UA OX Box or PALMER PDI03, etc, then out of the attenuator/load box 1/4" to speaker out to a 1/4" male speaker cable, that then attaches to the speaker leads of one of the Jensen speakers... The desired results:

1- To be able to crank the bassman to generate great overdrive tone, and be able to attenuate it to bedroom levels
2- To be able to record said tone from the attenuator/load box's line level outputs, i.e.: XLR or 1/4" line level outputs

My thoughts/questions:

- Given the very cool sounding 4 individual output design of the amp, would my approach in any way interrupt or hurt the amp in any way?
- Would the tone suffer in any way?

Your thoughts, ideas, experiences, very much welcomed...

eddie


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Post subject: Re: Fender Bassman 59 Reissue LTD and Attenuator/Load Boxes
Posted: Sun Nov 24, 2019 6:23 pm
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The 4 jacks are all wired in parallel -- electrically the same as one jack. So yes, you can use any one of them by itself. Some google sources say most RCA's are only able to handle 2A, which is about 30 watts into an 8 ohm load -- not sure what the current would be into a 2 ohm load. I might make a custom cable with 2 or 4 RCA plugs connected to one 1/4" phone plug just to be safe.

(Many RCA to 1/4" adapters are designed for preamp/line/headphone levels. If you use an adapter be sure it can handle at least 60 watts. Cranked, distorting tube amps can usually put out more power than their clean ratings suggest.)

The output transformer needs a 2 ohm load. (Four 8 ohm speakers in parallel is 2 ohms.)

Palmer PD103 is a load box/DI only. It has no speaker output. You can only use it for recording or to drive another amp.

OX is 4/8/16 ohm switchable input. May stress your 2 ohm amp. (Or the OX.)
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If you can find an attenuator that works with 2 ohm amps and if a single RCA can handle the full output (or you rig up a connection that uses several or all of the jacks), you can do what you're hoping.
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According to Switchcraft's ratings, phone plugs aren't guaranteed to be safe for high power applications. But obviously they are.

So a single RCA would most likely be safe.


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Post subject: Re: Fender Bassman 59 Reissue LTD and Attenuator/Load Boxes
Posted: Mon Nov 25, 2019 3:43 am
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Location: Province de Québec, Canada
I have a Weber Mass attenuator wich work on all speakers's ohms 2 , 4, 8 , 16 ohms


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Post subject: Re: Fender Bassman 59 Reissue LTD and Attenuator/Load Boxes
Posted: Mon Nov 25, 2019 4:41 pm
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Oh, and Weber sells a Bassman adapter kit that connects the amp to an attenuator, and the attenuator to the speakers.

Note that they use 2 RCA plugs to handle the output of the Bassman.

Much safer/more reliable than the RCA/phone adapters.

https://www.tedweber.com/bmh


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Post subject: Re: Fender Bassman 59 Reissue LTD and Attenuator/Load Boxes
Posted: Mon Nov 25, 2019 5:03 pm
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Thank You both 'stratele52' and 'strayedstrater' (great names)...

Intriguing electronics concept of creating a 4 or 2 RCA cable to a single 1/4" switch craft (the best in my opinion)... As i was searching for BASSMAN RCA wire harnesses, i.e.:

https://www.ebay.com/itm/A-59-Fender-Ba ... 2617403186

Coincidently, I too, found the Weber Bassman Adapter cable setup:

https://www.tedweber.com/bmh

With the Weber wire harness, I assume 2 of the speaker outputs from the Bassman are left plugged to nothing? I would think that they may need a load of some sort, i.e.: Dummy plug with a large enough resistor in it to simulate a speaker load...

Again thank you both...


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Post subject: Re: Fender Bassman 59 Reissue LTD and Attenuator/Load Boxes
Posted: Mon Nov 25, 2019 7:18 pm
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Correct, 2 of the 4 speaker jacks are left disconnected with the Weber. No problem.

The amp has 2 power tubes in push/pull with one output transformer. It's a mono output.

All of the jacks have their "+" connected to one end of the output transformer, and all of their "-" connected to the other end.

The amp doesn't care if there's one jack, 2 parallel jacks, 20 parallel jacks. It doesn't care how many are plugged in, no matter how many jacks there are. All it cares about is having a matching impedance load.

You could hook all the speakers together, then use one jack to connect them. (Like a Super Reverb 4x10.)
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If you use 1 jack, all 45 watts (maybe 65 peak) runs through that one jack.

RCAs weren't designed to handle high power. Weber uses 2 of them, so each handles 22.5 watts, for an extra measure of safety.

That's why Weber says you can stick the 2 plugs into any of the 4 jacks. All the jacks are connected together.
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There isn't anything magic or special about the 4 jacks -- they aren't "independent signals". RCAs are cheaper so he used them on the earlier, less powerful amps, then just added extras to handle the bigger amps.

Then when they introduced even more powerful amps he switched to phone jacks. And they became the industry standard, even for 15/20 watt amp where a single RCA would be sufficient.


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