Fostex f120a vs fx120 vs fe108ez?

[Jim Shearer]

Hi KM,

Here is the ST-35 built from the Dynakitparts with their BCU (bias control unit) upgrade and upgraded I/O connectors. An excellent kit with excellent support. I had one small question, so I emailed Dynakitparts and received a reply within the hour!

It powered up and is running with no problems. Sounds very good, although I am told that the sound should get even better with a few more hours on it.

The pic of the bottom during assembly is poor because light level was low & my phone doesn’t have a flash. In the second pic, you can see the BCU board in front of the power transformer.

Cheers, Jim

[chrisb]

Originally Posted by Jim Shearer

Hi KM,

Here is the ST-35 built from the Dynakitparts with their BCU (bias control unit) upgrade and upgraded I/O connectors. An excellent kit with excellent support. I had one small question, so I emailed Dynakitparts and received a reply within the hour!

It powered up and is running with no problems. Sounds very good, although I am told that the sound should get even better with a few more hours on it.

The pic of the bottom during assembly is poor because light level was low & my phone doesn’t have a flash. In the second pic, you can see the BCU board in front of the power transformer.

Cheers, Jim

whadya think your final total cost was on this project?

[Jim Shearer]

The kit with upgrades plus the tubes adds up to nearly $700 (then add shipping).

I did the assembly with the assistance of Bob, my son-in-law's father (a recently retired TV station engineer). Bob had built many tube kits back in his youth, and was pleased to get involved in another such project. I ended up with a really nice amp for the F120a and nice memories of working with Bob on the project (which are priceless).

Cheers, Jim

[kmaier]

Originally Posted by Jim Shearer

Hi KM,

Here is the ST-35 built from the Dynakitparts with their BCU (bias control unit) upgrade and upgraded I/O connectors. An excellent kit with excellent support. I had one small question, so I emailed Dynakitparts and received a reply within the hour!

It powered up and is running with no problems. Sounds very good, although I am told that the sound should get even better with a few more hours on it.

The pic of the bottom during assembly is poor because light level was low & my phone doesn’t have a flash. In the second pic, you can see the BCU board in front of the power transformer.

Cheers, Jim

Jim,

Very nice indeed... and in the original style chassis as well. I still have a chromed ST35 chassis and new cover sitting about. I'm guessing they implemented an individual bias supply per output tube. Good solution. What output tubes are you running and what is the plate voltage and idle current?

Regards, KM

[Jim Shearer]

>>>>What output tubes are you running and what is the plate voltage and idle current?<<<<

The individual bias feature (replacing the cathode bias via a single resistor for all 4 tubes) is Dynakit's BCU upgrade.

OK, here is where my ignorance becomes obvious.

I used the Dynakitparts recommended supplier, Antique Electronic Supply, and chose the ‘upgrade’ tube set: two NOS GE 7247 and matched quad of JJ EL84 (all marked 22/5.4). The assembly manual didn’t ask that you measure the voltages directly on the tubes. All I can tell you is what the manual says is normal (from the diagnostic section, which I didn’t need to use).
For the EL 84: pin 7: 370; pin 9: 375

You now see why I chose a kit rather than do a scratch build.

Cheers, Jim