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RE: Tube amp for EMI DLS 529 Dangerous Loudspeaker?







Simply because of the out of production 7355 O/P tubes, I'd avoid the H/K A500. Perhaps a conversion to EL34 category tubes, with "reissue" GL KT77s or less costly EH 6CA7s as prime contenders can be undertaken.

There are several things about the A500 that (IMO) need tending to besides "unobtainium" O/P tubes.

1. The "Cheap Charlie" method of DC filaments for preamp tubes is employed, where the heaters form part of the O/P tubes cathode bias network. H/K had plenty of company in using the method, which, frankly, SUCKS. :>(( The O/P signal modulates the preamp tube heater current.

2. PECs, an early form of integrated circuits, are employed. PECs frequently go bad and need replacement by discrete parts. H/K was not the only manufacturer to use PECs.

3. As is so often the case with units from this time frame, source selection should (IMO) be upgraded/modernized. Tape head I/Ps are passe and switches in mV. level signal lines are a source of trouble. A single set of I/P jacks should be directly wired into the low level magnetic preamp section, which is permanently configured for RIAA. All other I/Ps are line level and source selection is done only at line level. A suitable Lorlin brand rotary switch can be sourced from Mouser for approx. $5, but labor expense is present.

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Before you give up on your NAD, definitely replace the caps. in the speaker crossovers. What you hear may simply be the capacitors. Better crossover caps. will surely help with tubed power amplification too.

Dig around for methods which reduce SS amp damping factor. Aside from "bad" crossover caps., the "Dangerous" speakers could be over damped.


Eli D.


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