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    Recommended amp switch box btwn a SS and a Tube amp (for one set of speakers)

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    tajanes

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    Recommended amp switch box btwn a SS and a Tube amp (for one set of speakers)

    Post by tajanes on Fri Nov 23, 2018 5:19 pm

    The main issue I have come across is the need for the tube amp to always have a load… also would be great if included adjustable output to balance the levels to the amps

    Not so much to be used as an A/B test unit (as flipping tubes on and off cause havoc), but when watching TV (if not a concert, etc.) no need to warm up the room with a tube amp…

    Can I assume using Y splitters from the pre-amp signal out to both amps – where only one on at a time- is not as issue? Or do both the input and outputs need to be completely separated?

    Thanks,
    Andy

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    peterh

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    Re: Recommended amp switch box btwn a SS and a Tube amp (for one set of speakers)

    Post by peterh on Fri Nov 23, 2018 7:26 pm

    tajanes wrote:The main issue I have come across is the need for the tube amp to always have a load…  also would be great if included adjustable output to balance the levels to the amps

    Not so much to be used as an A/B test unit (as flipping tubes on and off cause havoc), but when watching TV (if not a concert, etc.) no need to warm up the room with a tube amp…

    Can I assume using Y splitters from the pre-amp signal out to both amps – where only one on at a time- is not as issue? Or do both the input and outputs need to be completely separated?

    Thanks,
    Andy

    If you solder a 100ohm 5w resistor inside the amp across ground and the 8 ohm outlet the
    tubeamp should be able to cope with open output, at least momentarily.
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    tajanes

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    thanks, and re the Y spliter into both the tube and SS amps..

    Post by tajanes on Sun Nov 25, 2018 2:41 pm

    will keeping both amps' inputs connected to the preamp (via the Y splitter) cause any problems? i.e. one amp will be on the other off but still have a common input chain- or do I need to disconnect the inputs as well?

    and re the resistor, do I need one across to the 4Ohm out as well as the 8?

    thanks
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    deepee99

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    Re: Recommended amp switch box btwn a SS and a Tube amp (for one set of speakers)

    Post by deepee99 on Sun Nov 25, 2018 3:33 pm

    It would be informative to know why these amps need a load for testing purposes. What gets hurt if you don't use one, and why? Perhaps Bob L. or Roy M. could give us a little primer for dummies on why we need a dummy load.
    I just scrounged up the cheapest little 8 ohm speaker from my parts bin (i.e. the basement) for a load. Works fine for double-checking stuff like bias (within limits) and pwr supply voltages.
    Ham transmitters will also emit huge plumes of smoke it not connected to a load (antenna in this case).




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    peterh

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    Re: Recommended amp switch box btwn a SS and a Tube amp (for one set of speakers)

    Post by peterh on Sun Nov 25, 2018 4:25 pm

    tajanes wrote:will keeping both amps' inputs connected to the preamp (via the Y splitter) cause any problems? i.e. one amp will be on the other off but still have a common input chain- or do I need to disconnect the inputs as well?

    and re the resistor, do I need one across to the 4Ohm out as well as the 8?

    thanks
    No, you only need some load to prevent dangerous peak voltages. An unloaded transformer
    can easily build up voltages high enough to cause flashover in tubesockets tubes or even worse
    inside the transformer itself. Loading with a fraction on any output will bleed most
    of the energy.
    To have the inputs paralleled is harmless, assuming that the driving preamp
    have low enough output impedance. If it's a transistor it will typically have < 50kohm and
    happily drive two or more amps in parallell.
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    tajanes

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    Re: Recommended amp switch box btwn a SS and a Tube amp (for one set of speakers)

    Post by tajanes on Sun Nov 25, 2018 4:39 pm

    great- thanks
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    Peter W.

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    Re: Recommended amp switch box btwn a SS and a Tube amp (for one set of speakers)

    Post by Peter W. on Mon Nov 26, 2018 10:10 am

    tajanes wrote:will keeping both amps' inputs connected to the preamp (via the Y splitter) cause any problems? i.e. one amp will be on the other off but still have a common input chain- or do I need to disconnect the inputs as well?

    and re the resistor, do I need one across to the 4Ohm out as well as the 8?

    thanks

    No. If you look at how output transformers are tapped, you will understand that you need only to use a single resistor.

    A few things in general - these are common-sense, not absolute. Most amps, tube or otherwise, will tolerate some abuse. But, only some. Best to avoid it altogether.

    a) Never, never short outputs - line level, speaker outputs, nor anything else. Line-level outputs from some pre-amps may be as much as 15 VAC, as a single example.
    b) Using a Y-connector from the pre-amp to more than one power-amp is a bad idea. This means that you are loading both amps, and the amp without a speaker load will suffer. There are any number of non-shorting (and shorting) switch-boxes out there that will do A, B, and A+B if that is what you want.
    c) Leading to: Never run an amp unloaded. Full Stop. With solid-state devices of some designs, this could be fatal within minutes. Tube amps take a little longer and depend on how hard they are being driven.

    Right off the shelf gets you this:

    https://www.amazon.com/TC-7240-Router-Switcher-Selector-Splitter/dp/B00KDQXITG/ref=pd_lpo_vtph_23_tr_t_2?_encoding=UTF8&psc=1&refRID=WHNFVDTWTNG13J5T6R78

    There are many more.
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    tajanes

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    Re: Recommended amp switch box btwn a SS and a Tube amp (for one set of speakers)

    Post by tajanes on Mon Nov 26, 2018 2:04 pm

    thanks for the info and ref

    jimmeq

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    Re: Recommended amp switch box btwn a SS and a Tube amp (for one set of speakers)

    Post by jimmeq on Tue Nov 27, 2018 11:58 am

    "b) Using a Y-connector from the pre-amp to more than one power-amp is a bad idea. This means that you are loading both amps, and the amp without a speaker load will suffer."

    Does this apply if the power to the amp is off? Or in the case of my SS amp, in standby?

    I have a TC7220 that I use to switch between my ST-120 and my SS amp. The amp I am not using at the time is either powered off or in "standby." I like being able to switch between sets of speakers too.

    https://www.amazon.com/TC-7220-Amplifier-Selector-Comparator-Crossover/dp/B00LNOAGZQ/ref=pd_bxgy_23_img_2?_encoding=UTF8&pd_rd_i=B00LNOAGZQ&pd_rd_r=a90d9c20-f25a-11e8-b188-2fb63616cf11&pd_rd_w=0VXeu&pd_rd_wg=UOXHY&pf_rd_i=desktop-dp-sims&pf_rd_m=ATVPDKIKX0DER&pf_rd_p=6725dbd6-9917-451d-beba-16af7874e407&pf_rd_r=09VCB88QCP4TSWY2XWQM&pf_rd_s=desktop-dp-sims&pf_rd_t=40701&psc=1&refRID=09VCB88QCP4TSWY2XWQM
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    Peter W.

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    Re: Recommended amp switch box btwn a SS and a Tube amp (for one set of speakers)

    Post by Peter W. on Tue Nov 27, 2018 12:38 pm

    [quote="jimmeq"]"b) Using a Y-connector from the pre-amp to more than one power-amp is a bad idea. This means that you are loading both amps, and the amp without a speaker load will suffer."

    Does this apply if the power to the amp is off? Or in the case of my SS amp, in standby?



    Generally, if an amp is not powered, there is no issue. It is when an amp is receiving signal, but is otherwise operating without a load that it becomes a problem.
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    tajanes

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    Re: Recommended amp switch box btwn a SS and a Tube amp (for one set of speakers)

    Post by tajanes on Wed Nov 28, 2018 10:26 am

    thanks for the recommendations, and solutions: i.e. Y in ok, but only one amp powered, a switch box, and potentially a resistor as a bit of extra security
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    peterh

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    Re: Recommended amp switch box btwn a SS and a Tube amp (for one set of speakers)

    Post by peterh on Wed Nov 28, 2018 10:39 am

    tajanes wrote:thanks for the recommendations, and solutions: i.e. Y in ok, but only one amp powered, a switch box, and potentially a resistor as a bit of extra security
    The permanent resistor is the most important of the above ! Hidden inside will keep
    the amp safe now and in the future.

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