DIY Another set of mono 300B amps or walking the diy plank 0-:
- Thread starter adnick
- Start date
Do It Yourself
adnick
Site Supporter
That’s a possibility, it’s really to make me think about it right now…the other one behind it, with the dovetails, is leopard wood and maple and the top would just fasten from underneath…..
That’s an interesting concept I’d not consider—-that’s why it’s good to get input from others here, some extremely creative individuals 👍
adnick
Site Supporter
Some of the mistakes made and /or issues encountered during my prototype build:
First one is a general fitment issue, related to using the Lundahl OPT and stock cover….
Placing the Lundahl 2785c, used the Lundahl website for the mounting hole pattern, then drilled then holes after I’d done the power transformer interference testing…Didn’t notice (lack of reading) that when one uses the Lundahl transformer covers, it changes the orientation and mount spacing of the transformer hold down screws
Was unfamiliar with the components making up the Rhum section of schematic, this caused me to leave out the “10 ohm hum pot”
Took the logical schematic too literally in relation to the 220R screen grid resistor, didn’t have it at the 300b tube….this was something that was obvious to me after Paul noticed my mistake, but it took a while to sink in…
Tried to use the Parts Connexion Diode Rectifier PCB, the one ordered couldn’t support the diode sizes needed, this was only obvious after receipt, not a big deal, more for informational purposes
Made an assumption that the C4S kit from Bottlehead came with the appropriate resistors for this application, mind you the resistor(s) values for this amp are clearly written on the schematic, this was the impingement to the amp functioning that literally took days to resolve, Paul discovered my mistake, once corrected the amp worked beautifully (hung my head in shame after this one)
Originally used a 1k 25 watt metal body resistor for the 300b, mounted in the wrong location for proper heat dissipation. Paul explained it would actually be better to use a lower rated wire wound resistor due to the metal housing ones degraded performance after heating up…
Next a few positive things:
Building an amp designed by @paul_b and having him as a guide/coach, undoubtedly the smartest decision I’d made 👍
Building a reference notebook with, parts list, schematic, tube data sheets, PT & OPT data specifications, and notes/advice from different amp builds—this includes several “how to” notes from other threads
Making copies of the schematic, tube data sheets, ect to hang in front of me during the build for reference/notes
Using the Schematic to check off completed tasks in real time
Made drawing of the tubes with their PIN numbers as the appear upside down (how they are viewed during the build process)
One could probably knock me for building a prototype/mockup version, without breadboarding it first, but this was a conscious decision…the actual builds are yet to come and this first one will be the guide.
Have a couple of pages of notes on minor changes/clean up work the actual builds
Probably forgot something, unlike Roger’s Ranger’s
One can find pictures of the manual contents in a previous post but here’s the cover for reference
First one is a general fitment issue, related to using the Lundahl OPT and stock cover….
Placing the Lundahl 2785c, used the Lundahl website for the mounting hole pattern, then drilled then holes after I’d done the power transformer interference testing…Didn’t notice (lack of reading) that when one uses the Lundahl transformer covers, it changes the orientation and mount spacing of the transformer hold down screws
Was unfamiliar with the components making up the Rhum section of schematic, this caused me to leave out the “10 ohm hum pot”
Took the logical schematic too literally in relation to the 220R screen grid resistor, didn’t have it at the 300b tube….this was something that was obvious to me after Paul noticed my mistake, but it took a while to sink in…
Tried to use the Parts Connexion Diode Rectifier PCB, the one ordered couldn’t support the diode sizes needed, this was only obvious after receipt, not a big deal, more for informational purposes
Made an assumption that the C4S kit from Bottlehead came with the appropriate resistors for this application, mind you the resistor(s) values for this amp are clearly written on the schematic, this was the impingement to the amp functioning that literally took days to resolve, Paul discovered my mistake, once corrected the amp worked beautifully (hung my head in shame after this one)
Originally used a 1k 25 watt metal body resistor for the 300b, mounted in the wrong location for proper heat dissipation. Paul explained it would actually be better to use a lower rated wire wound resistor due to the metal housing ones degraded performance after heating up…
Next a few positive things:
Building an amp designed by @paul_b and having him as a guide/coach, undoubtedly the smartest decision I’d made 👍
Building a reference notebook with, parts list, schematic, tube data sheets, PT & OPT data specifications, and notes/advice from different amp builds—this includes several “how to” notes from other threads
Making copies of the schematic, tube data sheets, ect to hang in front of me during the build for reference/notes
Using the Schematic to check off completed tasks in real time
Made drawing of the tubes with their PIN numbers as the appear upside down (how they are viewed during the build process)
One could probably knock me for building a prototype/mockup version, without breadboarding it first, but this was a conscious decision…the actual builds are yet to come and this first one will be the guide.
Have a couple of pages of notes on minor changes/clean up work the actual builds
Probably forgot something, unlike Roger’s Ranger’s
One can find pictures of the manual contents in a previous post but here’s the cover for reference
adnick
Site Supporter
Very kind of you ….
Well I certainly left off all the second guessing myself when there wasn’t any sound coming out
I’m also contemplating changing the position(s) of the 300b& 6k6, don’t think there’s necessarily any issues with it as is, it would just make the internals cleaner/easier to layout….
Wardsweb
Site Supporter
It is all part of the journey.Very kind of you ….
Well I certainly left off all the second guessing myself when there wasn’t any sound coming out
I’m also contemplating changing the position(s) of the 300b& 6k6, don’t think there’s necessarily any issues with it as is, it would just make the internals cleaner/easier to layout….
adnick
Site Supporter
I’ll get some together, but it’s simple because these gauges have faceplates so the only issue was finding a gasket to space out the faceplate and keep the light from shining out 360 degrees….used a rubber o ring, the LED is behind the lower portion of the faceplate,here’s a picture of a gauge
I went through this process recently with some new production Chinese meters that didn't have backlighting originally. I found that sanding amber LEDs with 40 grid sandpaper really diffused the light nicely. I also ended up putting two LEDs in series on each meter, as that really broke up the hot spotting and patterns that I got out of one. I ended up melting a couple of small holes in the bottom of the meter up against the back side of the faceplate to poke them through.
I think those look far better than the ones I did. I did put a pot in the circuit so I could adjust the brightness. The effect is not as glaring as in the pictures. I pulled my source from the 6.3VDV to the input tubes. I'm going to revisit my lighting build I think.
adnick
Site Supporter
That’s some good info, I’m going to employ some of those techniques….. 👍
The bulbs went behind the metal faceplate or in front between the clear plastic and the dial faceplate?
