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DIY vacuum valve amp | by --Kei--
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DIY vacuum valve amp

Valves:

Mullard EF86

GE JAN 6CG7

Electro Harmonix 6CA7EH

Sovtek 5AR4

 

Iron:

Sowter UA21 outputs

Primary Windings mains

VVT chokes

 

I've made some changes to the design as the gain was too high and I couldn't resort to simply increasing the feedback in order to reduce it. The change allowed for a reduction in open loop gain and also a small increase in feedback level too. This successfully dropped the gain from 49.54dB open loop and 33.26dB closed loop to 45.77dB open loop & 25.87dB closed loop. That also took feedback from 16.5dB to 19.9dB.

 

Current schematic:

www.flickr.com/gp/39959182@N05/Vb7382

 

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Taken on September 16, 2020