Hello all,
I have recently completed my RH807, a design by Alexsander Kitic which is a S.E. amp using a short feedback loop between the plates of both the driver (12AT7) and 807 output tubes. I built it as per the schematic but found the G2 voltage was higher than allowed according to the datasheets so made a voltage divider and feed G2 with 250V and bypassed with a huge 330uF cap which is all I had.
This being said, I did play it as per the schematic for a couple days with no ill effects, the 807 is a transmitting tube so should be as tough as the proverbial old army boots.
Anyway, on first build I used RCA 6l6GC’s then GEC KT66’s and then the 807’s.
The 6L6GC’s were nice but I found them a bit aggressive or rough in tone, then tried the KT66’s which were much nicer, the 807’s however are in another league altogether, this was good because I had to change the sockets of course and would have had to have made make some adaptors to return to the octal sockets. The 12AT7’s were a new production JJ? maybe, I forget now and an old Westinghouse, not much difference I found.
This is my first taste of the 807 and have read a lot of good about them and its well deserved praise indeed, the best part is that they are cheap, I paid 15 pounds for five new tubes or valves I should say via ebay.
I had built another of Alex’s designs a couple months ago, the same scheme but using the EL84 which is one my favorite tubes and this 807 is easily as good and I think better. The comparison is a bit unfair as the EL84 used 125ESE’s for the outputs and the 807 is using Softone RW-20’s.
I was so impressed that I bought a pair of Lundahl outputs for rebuilding the EL84 version.
Anyway, before this post gets too much longer, if it means anything I highly recommend this circuit, well worth the effort.
Andrew
I have recently completed my RH807, a design by Alexsander Kitic which is a S.E. amp using a short feedback loop between the plates of both the driver (12AT7) and 807 output tubes. I built it as per the schematic but found the G2 voltage was higher than allowed according to the datasheets so made a voltage divider and feed G2 with 250V and bypassed with a huge 330uF cap which is all I had.
This being said, I did play it as per the schematic for a couple days with no ill effects, the 807 is a transmitting tube so should be as tough as the proverbial old army boots.
Anyway, on first build I used RCA 6l6GC’s then GEC KT66’s and then the 807’s.
The 6L6GC’s were nice but I found them a bit aggressive or rough in tone, then tried the KT66’s which were much nicer, the 807’s however are in another league altogether, this was good because I had to change the sockets of course and would have had to have made make some adaptors to return to the octal sockets. The 12AT7’s were a new production JJ? maybe, I forget now and an old Westinghouse, not much difference I found.
This is my first taste of the 807 and have read a lot of good about them and its well deserved praise indeed, the best part is that they are cheap, I paid 15 pounds for five new tubes or valves I should say via ebay.
I had built another of Alex’s designs a couple months ago, the same scheme but using the EL84 which is one my favorite tubes and this 807 is easily as good and I think better. The comparison is a bit unfair as the EL84 used 125ESE’s for the outputs and the 807 is using Softone RW-20’s.
I was so impressed that I bought a pair of Lundahl outputs for rebuilding the EL84 version.
Anyway, before this post gets too much longer, if it means anything I highly recommend this circuit, well worth the effort.
Andrew
