Proposed Mark III Layout

MontanaWay wrote:

TN Allen wrote:Before looking more carefully at the Tubes4hifi MK3 photos and noticing the quad capacitor is 80-40-30-20, I bought a quad capacitor similar to what was used in the original MK3, 30-20-20-20. I'm wondering What advantage the 80 & etc capacitor provides over the original?

a lot of components used in the original Dynaco amps as well as preamps were a compromise, mainly based on cost savings. The 30-20-20-20 is probably absolute minimum. Going somewhat higher, ie 80-40-30-20 gives the amp more 'stored energy', having to rely less just on the transformer to power the unit.
Of course, having said that, there is a limit too, going to high is no good either. I would NOT use the 30-20-20-20 in this amp, so you'd be better of getting the 80-40-30-20, get the higher voltage unit too, costs a but more, but gives you that margin, especially during power up!

TN Allen wrote:

MontanaWay wrote:

TN Allen wrote:Before looking more carefully at the Tubes4hifi MK3 photos and noticing the quad capacitor is 80-40-30-20, I bought a quad capacitor similar to what was used in the original MK3, 30-20-20-20. I'm wondering What advantage the 80 & etc capacitor provides over the original?

a lot of components used in the original Dynaco amps as well as preamps were a compromise, mainly based on cost savings. The 30-20-20-20 is probably absolute minimum. Going somewhat higher, ie 80-40-30-20 gives the amp more 'stored energy', having to rely less just on the transformer to power the unit.
Of course, having said that, there is a limit too, going to high is no good either. I would NOT use the 30-20-20-20 in this amp, so you'd be better of getting the 80-40-30-20, get the higher voltage unit too, costs a but more, but gives you that margin, especially during power up!

MontanaWay,

Thanks. This one:     http://www.dynakitparts.com/dynakit-products/capacitors/MULTI-ELECTROLYTIC-C

TN Allen wrote:sKiZo suggested that if I might want to use a GZ37 in the future, and that I should leave enough space for this larger tube. Would the GZ37 be suitable for the mono amp? At around $150 from TubeDepot, I might pass on it, or wait to use it in another stereo amp.

Can the quad-capacitor be located inside the chassis?  

The tube spacing remains a dilemma, looking at the original design, and various other KT88 amp designs, spacing is close, really close in some cases. Is there evidence this does require replacing tubes more frequently?

TN Allen wrote:Here are two photos of a revised layout, ...  but would like to keep the layout reasonably compact. I'd appreciate any further comments or suggestions.

nmchiefsfan wrote:If you are going to locate the quad cap underneath, would it not be easier to use discreet components?

TN Allen wrote:Would anyone know what voltage rating for the .02uF for the small disc shaped capacitor soldered to the terminal strip between the red-yellow and yellow-green wires.

Also, the instructions I have show the yellow wire from the output transformer connected to the NFB eyelet on the new Tubes4HiFi PCB, I think I have this correct. But this seems to eliminate the 16 Ohm output. If possible, I'd like to retain the 16 Ohm output. Is there a way to do this?

Thanks in advance for any suggestions.

TN Allen wrote:I may yet finish this project. It is wired, though I overlooked the 2 1K resistors on pins 5&6 on the KT88 sockets. I don't know how I overlooked them, but did. I have 1K 1 Watt resistors.

Unfortunately I tried the amplifier without these, although only so far as checking to see if the filaments had current, which they did, and then with the rectifier and KT88 tubes in place and powered, but without the 12AU7 tubes in their sockets. The 3Amp fuse blew, hopefully avoiding any other damage.

I plan to solder in the 1K resistors, and add 4007 diodes to the rectifier socket, even though I'm using a SS rectifier substitute for the 5AR4.

I suspect there may be damage beyond the blown fuse. Would anyone have any suggestions for what I should check for damage? And, before soldering the resistors and diodes in place, how should I safely dissipate any residual current in the quad capacitor?

This has been a good project, I've learned quite a bit doing it. There are quite a few things I'd do differently were I to do another MK lll, but nonetheless it's been a good learning experience.

stewdan wrote:TN Allen ..... Bob Latino has posted on the Web a colored wiring diagram for the Mark III which has all the colors of the Transformer Wirings and might be of use to you?!

Do a Google Search for "Latino Mark III Wiring" and you will pull it up.