Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TIMBO on May 20, 2013, 04:10:11 am
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Hi guys, This is one of our locally made amps from long ago. http://www.grouseguitars.com.au/sold/morepics/moremoodyba40.htm (http://www.grouseguitars.com.au/sold/morepics/moremoodyba40.htm) I have posted this for no real reason other than it amazes me the ideas amp builders come up with back then and with a long list of tubes to play with are willing to stick them in their amps.
I have not seen this (6BL8) in a (if I say phase splitter I might be wrong) before.
Have any other amp builders use this type of THINGY, any pros/cons. Thanks :icon_biggrin:
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Dynaco Mark III, Sunn, and some Ampegs use a pentode/triode. Probably others too. The circuit is basically the same but Dyna and Sunn preferred 6AN8 and Ampeg liked 7199. You can also find that circuit in the hifi audio amp circuit in the back of the RCA tube manuals.
I've never seen the 6BL8 used before. The pentode is just a voltage amplifier and the triode is the split load phase inverter.
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During the 1960's there were a number of Australian guitar amplifier manufacturers, including Moody, Fisonic, Goldentone and Maton. These amp builders disappeared in the 1970's as changes in import duties made it impossible for them to compete against amplifiers from overseas.
At the time they were in business, imported audio valves such as 6L6's and 6CA7's were quite expensive, so wherever possible they would use locally made television valves. It was not uncommon to see 6BL8's, 6AN8's or 6U8's used in cathodyne phase inverters. Similarly, 6DQ6's and 6CM5's were often used as output valves.