ampage Tube Amps / Music Electronics	For current discussions, please visit Music Electronics Forum.

ampage archive

Vintage threads from the first ten years

Re: I know a way to do it.

:

12/13/1999 3:27 PM
Don Symes	Re: I know a way to do it. Good. I knew there was a smart way. Grounding the input of the head you aren't using means the dummy load can be relatively low-wattage (say 10-25W), too.

12/13/1999 5:06 PM
Randall Aiken	Yeah, but those gold-anodized 50W Dale resistors are relatively cheap insurance. I had an impedance selector switch as well, to switch the dummy load to 4, 8, or 16 ohms. That way, if anything went sadly wrong with the relays, the dummy load would protect the amp. Randall Aiken

12/13/1999 6:32 PM
GFR	Randall, Do you take any special care so that the amp is not unloaded even for a short period of time (like first connecting the dummy load and then disconnecting the speaker)?

12/14/1999 12:46 AM
Randall Aiken	Nah, these relays are damned fast. I don't think the tiny (milliseconds) switchover time when one switches from load to speaker and the other from speaker to load is anything to worry about. I thought about a "make before break" switching delay circuit, but it didn't seem worth the trouble at the time, so I just went with the simpler circuit. Randall Aiken

12/13/1999 6:34 PM
Don Symes	Completeness is a _very_ good thing. Hope that schematic goes up soon.

12/14/1999 4:24 AM

Aren't there some old hi-fi amps that use fairly high value resistors across the OT? You know, like on your home stereo that has "A" and "B" speaker outs? That way the OT and output circuit is never shorted or open-circuited? Then you could use a SPDT relay or switch without fear of frying anything, right? Seems simple to me if you're going for the "combo with open-back" for rhythm and "closed-back" for lead that you could get away with a minimum of parts. I recall an old thread on the archives many moons ago. Tboy, where are you now?

Farrow
http://surf.to/pharaohamps
http://www.skybolt6.com

12/14/1999 6:54 AM
Randall Aiken	The schematic is now posted. The HeadSwitch schematic is now up on the DIY section of the Tech Info pages at http://www.aikenamps.com - have at it! I added some suggested readily available (from DigiKey) relay part numbers, which are different than the ones I used, but should work fine. Randall Aiken

Page 2 of 3