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Another Rowe 4359 amp rebuild

Thank you for posting the reference information on the EFB/IBBA boards - seems easy enough to knock out on bits of perf-board.

Nice specs- and decent low distortion, with worn tubes no less. Great build!

The 6L6GB tubes are pulling .9A filament instead of the .8A that the 7868 tubes did- I wonder if that is part of why the filament is running lower? But, perhaps Rowe also did this to extend tube life given the amp was basically always on.
 
At those voltages and transformer load its basically datasheet conditions for a 6L6, not a bad place to be

I wonder if these ran any 6v light strings. If so I'd expect losing them would easily make up for the extra little bit of heater draw.
 
A glamorous shot with the new damper diode. Nice tubes. The 6CG3 is 350mA rated. A pair of them for a full wave setup is a bit heater hungry but not a big deal for DIY. Super slow voltage ramp up. Especially with this one on 5V instead of 6.

IMG_6892.jpeg
 
I dropped the bias current from 45mA to 40mA and the power supply voltage of course increased. My post with the voltages and THD numbers was before I decreased the bias. With the increased voltages the power at 1% THD also increased a small bit. I now have 382V B+, 377V at the 5881 plates and 277V screen. I forgot to measure the supply to the front end stages. It probably increased by 10-15V which shouldn't hurt the performance.
 
Revised amp schematic and added schematics for EFB and IBBA boards. See post 32. I thought I should keep them in a single post and update as required so there weren't multiple versions in the thread.
 
Thank you for updating the schematic.
Where did you snag that fancy chassis mount 12-pin compactron socket?
 
The compactron socket is Chinese from ebay. There is a seller in Florida that has them on-shore. They aren't great but seem to work ok so far. There are other US or European made compactron sockets on the auction but they can be rather expensive. I have some other US made old stock sockets but hoarding them for some better project.
 
I have a Rowe R-4359a floating around somewhere in Missouri and hope to have in sometime this month. Found it fairly cheap, thought it might be interesting to experiment with for no good reason. Then I found this thread. It is similar to the one mentioned above, but looks like a SS rectifier plugged into the socket. Looks factory. It also looks like the heater wires are in place if a tube is used, but wont know until it arrives. Big stupid question, what did these amps come from? I'm kinda thinking maybe an organ or jukebox, but am kinda at a loss.
 
I think I've seen one of these with a factory solid state plug-in rectifier. Maybe thats the -A version?
 
gadget73 said:
I think I've seen one of these with a factory solid state plug-in rectifier. Maybe thats the -A version?
Click to expand...
You are correct. I have a R4359A, and the chassis is labeled for a 1N2389 octal base SS rectifier. I'm running a Tube Depot Solid State Rectifier (SSR) in mine, along with an added thermistor to limit the inrush.
 
I used JLCPCB which is in China. Before tariffs and shipping cost increases it was quite fast and reasonable to order a batch of boards. I had Sheldon Stokes’ cap boards made and a bunch of other boards.
 
I should have a set made, my next amp will use EFB and I have an amp with a DIY bias/balance but its not as neat. I generally prefer through-hole mounted pots and test points for adjustments when practical though, just so i don't have to flip the thing over to set stuff up. My Fisher 600 for example needs the bottom removed and a set of minigrabbers to check and adjust things, which means I set the bias once a number of years ago and haven't even checked it since.
 
I built a Fisher 500c clone last year using original transformers. I added these EFB and IBBA boards to it and made the IBBA with the pots on the reverse side so I could adjust it from the top deck with some pin jacks. You can zoom into this picture and see them. Getting a nice row of 4 holes took a little setup on the drill press. This Rowe project being a retrofit didn't really have the space to fit it in like this, but there isn't a bottom plate so not too difficult to set it on the side and adjust. Probably could have made it work from the top but would need the 5 pin jacks squeezed in too.
Top with sockets.jpeg
 
Reinstalled the mounting brackets. I ground the rivets and punched them out so I could reverse them. Got them reinstalled with some small amp feet. Only thing left to do is permanently install the feedback and tuning components which are still tack soldered.

IMG_6894.jpeg
 
gadget73 said:
I should have a set made, my next amp will use EFB and I have an amp with a DIY bias/balance but its not as neat. I generally prefer through-hole mounted pots and test points for adjustments when practical though, just so i don't have to flip the thing over to set stuff up. My Fisher 600 for example needs the bottom removed and a set of minigrabbers to check and adjust things, which means I set the bias once a number of years ago and haven't even checked it since.
Click to expand...
ill go in with you on some —i cpuld use at least two.
 
I just created a cart at JLCPCB for 10ea IBBA and 10ea EFB boards. The sets of 10 were $5 each or $10 total but the shipping was about $39 and who knows about import duties these days. Even so, $50 for 20 pc boards may not be a terrible deal if the tariff or duties aren't too bad.
 
nerdorama said:
I just created a cart at JLCPCB for 10ea IBBA and 10ea EFB boards. The sets of 10 were $5 each or $10 total but the shipping was about $39 and who knows about import duties these days. Even so, $50 for 20 pc boards may not be a terrible deal if the tariff or duties aren't too bad.
Click to expand...
hey if theres a group buy, id like 3 of each. anyone else?
 
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