fred.violleau wrote: ↑Sun Jun 14, 2020 12:42 pm
I love to see how everyone approach a build. I now tend to do all the peripheral wiring first as I think it is easier to organize the lead dress and which cable is going where. And then I start to add things on top of it. You seem to be doing a bit of both at the same time Rootz! Nice build BTW!
Fred.
Hi Fred, I don’t think there are many smart and efficient ways to wire an amp haha. I think your method is best. Stacking layers on top of each other. I tend to do that too, placing the boards last. For this build all wires to the PS board will go over the top edge of the board, not from the under side. This had the advantage that disassembling the board is rather easy. So easy modding.
I usually pre cut the wire to length and test fit them all. Hence the boards go in and out of the amp again and again .
Anyway, I’m about to wire the OT primaries and secondaries. Pt is done: wired to the rectifier/bias and relay power boards. Then it’s time to do most of the coax for the od and reverb, essentially everything that goes to either a socket or the relay board. Then the PAB. By then I’m getting to wiring in the PS and preamp boards. I’m working painfully slow, so it will take many more evenings...
rootz wrote: ↑Sun Jun 14, 2020 10:47 pmSnap!! There goes my 40 years old switchcraft...
Ouch...
The best way to bend back metal is by hammering it, NB. That is "sending back" the stress/strain to where it came from, rather than adding to the existing. Easy to say... as usual... but you got the idea...
Smoke test passed! PSU is what it should be and what I expected.
528 VDC for the plates, 6.8VAC for the power tube filaments, 14.5VAC preamp filaments, -50 to -66 VDC bias, 13.5VDC relays/leds. Looks good to me. Relays are g5v-2-h1. Those can take 180% of 12v. With a pedal the less will be in series, so I’m keeping it close to 12v@15mA.
On to the wiring of the preamp board and then it’s pretty much done
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Done with all the wiring and soldering. Holy shite, that was an awful lot of work!!
Now on to the testing phase. It actually don’t know how the amp will sound and if the reverb will have the strength I’m looking for. Will it work at all? No idea! Easy to make some dumb mistakes building a Dumble.
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There aren’t any black wires connected to the power tube sockets, apart from the sole jumper I used from the tag strip to the socket for the filaments. The rest is just heat shrink on the bias check resistors and fly back protection diodes.
Tonight I will check all the wiring to see if there’s any defects or loose connections.
And it’s alive!! Just one small mistake: swapped two wires around around the loop and master volume. It was 10.30 pm so not much room to test at any decent volume. However, I like what I hear. Clean with a strat is wonderful. More compression when compared to a low plate classic. Some serious low end thump from the power section. Reverb is just wonderful. I think I can now drive the tank to the max with the half ecc81 driver. Can’t wait to turn up the master and really give it a spin.
The plates idle @ 515-520 V at 30mA. V1 is around 210V. Power tube filaments are at 6.6V. All a bit high. Might connect the 240V primary on the power transformer instead of the 220V tap.
Another worry I have is that amp gets bloody hot. The back of the amp around the power tubes must be getting 60 degrees Celsius. Hot to the touch and I couldn’t place my hand on it for more than a couple of seconds. Does that sound normal? Do I have a potential problem here or should I be good. I could add a fan of course.
I’d Definitely go for the 240V primary, which should get you down to 475-ish B+ and just about 6.3 on the filaments. A fan is probably the only way you are going to get it to run cooler. Pulling air in from the bottom of the cab seems to be the best option, maybe rectify filament voltage to run it.
Thanks Martin, that confirms most of my thoughts. Marcus had similar problems on one of his amps. Seems to be a common problem that heat builds up. I think I can full wave rectify the 6.3V for the power tubes and get around 9V for a big 120mm fan. Rectifier will be floating with respect to ground. Fan can probably be mounted on the front panel, that already has some large holes for extra cooling in it.
Now I’m need to find out where the 240V tap is. Luckily I didn’t cut hem short, but soldered the unused primary taps in two ‘blind’ eyelets on the power supply board. Should be simple to change that.
My 100W gets quite hot if it runs for a couple of hours. Blowing or sucking through the front grille is a possibility, but might collect dust. The space is limited too, because of the transformers. I was thinking the same re the floating DC. You could run a 12V fan on low voltage to keep the noise down.
Congrats on your new build rootz! Let us know which is your favorite our of the 2 amps or maybe each is very special in its own way!
I know a lot of the power transformers from twin reverb amps from the 60's and 70's ran very hot as well, couldn't keep hand on power transformers for more than a few secs and they ended up lasting several decades and then some. These are huge chucks of iron and can take a lot of heat.
I would definitely go for the 240v tap on the transformer this should cool things a bit.
I am planning a second Overdrive Reverb build and this time I will be using Marshall 100 watt power transformers.
Cheers!
Guy
Last edited by Guy77 on Fri Jun 19, 2020 1:53 pm, edited 1 time in total.
Guy77 wrote: ↑Fri Jun 19, 2020 1:47 pm
Congrats on your new build rootz! We will eventually need to know which is your favorite our of the 2 amps or maybe each is very special in its own way!
I know a lot of the power transformers from twin reverb amps from the 60's and 70's ran very hot as well, couldn't keep hand on power transformers for more than a few secs and they ended up lasting several decades and then some.
Cheers!
Guy
exactly. the hot Peavey trannies I have are 30 years old and going strong despite the heat. I haven't got round to installing a fan yet either.
i would love to add reverb to one of my ODS. that is something I'm going to look into after seeing your builds.
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