Comments for page: HF-20 Monoblock

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Posted by Steve L. July 05, 2012 - 02:58 pm
Hi again Wes, I just found the thread on Audio Karma. I see that the concern was for the lack of load on the power transformer, if you remove V2, instead of isolating the pin with heat shrink. Removing the tube, eliminates the 1.9W heater load, which the 12AX7 has. Since the total load on the 6.3V heater winding is normally about 19W, the voltage would not rise significantly, due to the removal of that one, low level tube. In fact it would help alleviate slightly, the fact that the HF-20 power transformer normally runs pretty hot. Thank you for giving me an opportunity to address the concern.

Posted by Steve L. July 05, 2012 - 02:36 pm
Hi Wes, Thank you for responding. I'm a bit puzzled by the concern which was expressed on the message board, because a transformer would not normally be involved with this. As was mentioned at the end of the article, the input impedance of the HF-20, used this way, should be about 77K. Virtually any hifi preamp will be able to drive that load.

Could you refer me to the posting, so that I might look into the concern a bit more?

Thanks, Steve

Posted by Wes July 05, 2012 - 01:55 pm
I just tried this with my HF 20's and I love it. I mentioned it on a message board and a concern was mentioned about how it might affect the load on the transformer. Any thoughts on that?

Posted by Steve L. May 06, 2012 - 12:34 pm
Hi James, The HF20 was made with a power switch on the Treble control. If yours has a separate toggle switch, it must have been added by an owner. It could be that the treble pot had to be replaced or the switch on it went bad. It's not so easy to find the right pot and switch combo for replacement, any more.

You mention that the knobs look really crusty. If that is the white mold that they often are seen with, it is easily removed with a toothbrush and 409 cleaner. With doing that and maybe a little plastic polishing, you can have them looking as good as new, pretty quickly.

Posted by James R.Powell III. May 06, 2012 - 12:09 pm
Hi, Patrick I didn't really do much to the amp. The knobs looked really crusty. I may try to restore them. I like the yellow gold knobs from amplifiedparts.com. I simply use the aux input, by using a high qualty RCA Monster cable with 1/4' adapter. I addede a Shure tube phono preamp just before the input to drive the input slightly. I have the amp connected to a MusicMan 4x12 cab. I have some various pedals to drive the amp. I wish I had a second Eico HF20! I plan to post a video documenting this amp. I plan to find another Eico HF 20 or get a similar lower watt amp. I have seen a Jet City Pico valve. It's only 5 watts has a similar look. Licensed by THD. THD has a few amps similar shape and cage style. Univalve and Bivalve.

Posted by James R. Powell III. May 06, 2012 - 11:55 am
I noticed my Eico HF 20 has an on/off switch. The other pics of them I have seen do not have a switch. Curious?


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