Vintage Asylum Classic gear from yesteryear; vintage audio standing the test of time.

---

[ Follow Ups ] [ Post Followup ] Thread: [ Display  All  Email ] [ Vintage Asylum ]

---

[ Alert Moderator ]

---

Re: dynaco mk3 vs eico hf-60

Posted by Bold Eagle (A) on May 11, 2007 at 17:34:23

In Reply to: Re: dynaco mk3 vs eico hf-60 posted by rcb on May 11, 2007 at 11:50:02:

I'm not sure what changes would be needed in the HF60 schematic for KT88's, but it's a good move.

Personally, I like the Dyna circuit. The phase splitter is self balancing and the accuracy of the split is only dependent on the matching of the matched pair resistors in the Mk II/Mk III schematic. The outputs in the Dyna are in a common cathode circuit and are also self balancing if the tubes are a matched pair. They ought to be in any circuit, anyway!

The voltage amplifier and phase splitter/driver circuits are fine if the distortion is low and the amp can be driven to rated output and has decent dynamic headroom.

I've owned the HF60, and once built a 50 watt amp based on a large, potted Chicago transformer. It used a Dyna output circuit and a Mullard voltage amplifier and phase splitter/driver circuit. It measured quite well and sounded exactly like my Dyna Mk II. The Dyna had better measurements at full power at the frequency extremes because of a better output transformer (less core saturation at low frequencies, and lower leakage inductance at high frequencies)so the power bandwidth was more extended. So much for the supposed differences in the voltage amplifier and phase splitter!

People develop strong biases toward certain circuits (I have my own) both positive and negative. I can accept that. What I can't accept is "circuit evangelism" where everything outside their favorite is torn down.

I do feel the best Dyna is the Mk II. (although I would use the GZ34 and put in a silicon diode to replace the selenium rectifier) I think it represents the optimum use of the transformers. It seems to me the Mk III is a "hot rodded" version, brought out to counter higher power ratings from competition. You can use KT88's in the Mk II for a richer sound, although I like the EL34's. The differences in the Mk II and Mk III are the 5U4 Vs GZ34/5AR4 rectifier, a slightly different cathode resistor in the output circuit, and an LC, instead of RC filter in the power supply. Decades ago, I back converted a MK III to a Mk II to have a matched pair.

Jeez! Now you've got me thinking about a project.

Jerry

This post is made possible by the generous support of people like you and our sponsors:

Signature Sound

[ Signature Sound Lounge ]

---

[ Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2024, Audio Asylum, all rights reserved ]

---

[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]

---