Quote:
P.P.S. Burnedfingers: "I thought the stock board was marginal at best" - you seemed to like it according to your posts on
www.diyaudio.com (once you'd replaced the old parts on the driver board)...?
Do you have a particular post in mind? There are probably one or two comments that I mention that changing parts made an improvement. If I was really impressed with the performance of the stock board then why would I change it? If you have something you would like to discuss please do email me and I would be glad to comment.
To those that find the bass response of the stock Dynaco enjoyable ... maybe you haven't experienced really good audio gear in your short term of audio. Bass is supposed to be tight, fast, and punchy. Unfortunately there are those that consider the boom boom of car stereo to be bass. Unfortunately because I have to play with high powered systems I have little tolerance for the sound of junk and I am highly critical of everything I listen too and therefore try to make things as good as possible.
In checking your cap..in some instances it is best to substitute the cap in question with a suitable loaner. If the cap in question is real leaky you may not see a performance improvement or any lowering of the hum. Do not exceed the value of your first cap because you may experience a flash over in the 5AR4 or damage it. You may also want to change out the caps in the bias circuit as it can also contribute to hum in the amplifier.
A nice modification for those interested in using other tubes would be to wire a switch and resistor in parallel with the 10K resistor in the bias circuit or better yet would be a -on-center off-on- switch. This would allow for two selections of resistance to be paralleled with the stock 10K resistor. Note only one resistance value at a time in each direction and a STOCK setting in the center detent. THis would allow for example KT 66's in one switch position, the stock EL34 position, and another selection such as 6BG6GA's in the last selection. Since the bias voltage and current are so low there would be no problem with the switch handling it.
In my opinion the best modification to ANY Dynaco Stereo 70 is the addition of individual bias controls for each output tube. There are some that would argue that it isn't necessary but as we know tubes do change and even the best matched tubes do NOT stay matched for very long.