PH-15 Battery mod

Quote from previous post from TM Madden 'To take it one step further as done in the Loesch style preamps, you can eliminate the voltage divider and cap entirely and just use a 9 volt battery to bias the triode'

I'm interested in this mod and I'm wondering who's tried it. I'm not sure how to implement it. Could solder three lithium cells in series or use a 9V battery (PP3 in UK). Assume I need to try to keep wiring to a minimum to eliminate pick up.

Any photos of battery bias in practice on the PH14/15 would be appreciated.

Hello,
Here's a rather poor photo of how I did the mod on my PH14. As you can see (hopefully), I desoldered one end of R5, where it connects to resistor R7, resistor R6 and capacitor
C2. R6 and 7 form a voltage divider, to derive the 9.1 volt bias on V1's grid. R5 is the grid resistor, which we want left in the circuit. You just connect the positive side of your 9 volt battery to the now free end of R5, and the negative side of the battery to the ground trace on the board, and there you have it. As you can see, I didn't worry too much about wire length, and I didn't have any noise issues.

Thanks for this. I had wondered if the wires from the battery connectors might pick up some mains hum . Have batt connectors on their way. Also have some Hashimoto HM-3 SUTs on way which I will probably mount inside the case. They have a good reputation and came at the right price c/o Fleabay.

I did the battery bias mod this afternoon. First impression was that it sounded a bit brighter and more detailed.
Once it had warmed up again I started to really enjoy the sound. I would love a switch to do a blind listening test
(girlfriend operated). Waiting for my Hashimoto HM-3 SUTs to be delivered when I will install them in the PH15 chassis. They are supposed to be very good. They came from Japan to our local ParcelForce (Farce) depot no trouble at all. If only I could get them delivered.

Thanks for sharing your experience with the battery bias modification. I had the same impression of more detail. You should have a really sweet preamp with the Hashimotos! I also just received a pair of Hashimoto transformers for a experimental project I am building.

TMadden wrote:Thanks for sharing your experience with the battery bias modification. I had the same impression of more detail. You should have a really sweet preamp with the Hashimotos! I also just received a pair of Hashimoto transformers for a experimental project I am building.

Really enjoying my listening. I think it was a very worthwhile mod, especially with a number of albums I've been listening to this afternoon.
Seriously considering importing a s/h Dynaco ST-70 now though it will need to be good to see off my Unison Unico.
Hope you let us in on the details of your project.