How did Hiwatt do dc power on the dr210?Is it a high gain amp?

[frank57]

I've been looking at this dr210 or sa210 and they have two diode bridges in there.
I want to finish off their schematic because it's not complete.
They left out some things.
It's also a very small amp and you can see the unusual
 assembly here:
1996 HIWATT SA210 Audio Brothers Assembly PT2

But how did they do the dc power stuff?

They also have 4 caps on the other bridge.
I tried to draw out their layout so far. I think r12 is 220k too.
Is it a high gain or low gain amp?
Might be a good project for someone with more experience to tackle.

[RicharD]

Have you researched http://www.mhuss.com ?  That dude is the "king" of HiWatts and he's super friendly.  Drop him a line, he'll help you out.

[sluckey]

But how did they do the dc power stuff?

The bridge with the caps is for the B+ (BTW, you drew the bridge backwards on the partial schematic) and the other bridge is for the DC filaments.

Is it a high gain or low gain amp?

Looks like enough gain stages to be called a high gain amp.

Hey, if that guy had removed the lower back panel, that video would have only been 3 minutes long. 

[frank57]

I drew it backwards? oops.
Which way is the right way?

I think for the dc power they used two caps of some kind and two 4.7k resistors.
Does that make some kind of sense?They're the two big ones right at the end of the preamp stuff, but I can't read the values.

[HotBluePlates]

Is it a high gain or low gain amp?

It depends on what you mean by "high gain."

The modern Hiwatt has (or had) a line of amplifiers called "Hi-Gain" which were distinct from the "Custom" line, which included most of the classic models typically associated with Hiwatt.

The SA210 was part of the "Custom" line; That said, I'd consider it a "high-ish gain amp" because there are 3 gain stages and a cathode follower ahead of the phase inverter. Look at the schematic you have to this point; the classic Hiwatt amps would have the master and tone circuit between V1a and V2b, plus an extra channel. The SA210 ditches the extra channel, and adds the leftover triode as a cathode follower ahead of the tone circuit. The tone circuit is changed from typical Hiwatt to something that more closely resembles a Marshall tonestack.

[sluckey]

I drew it backwards? oops.
Which way is the right way?

Flip it horizontally.

I think for the dc power they used two caps of some kind and two 4.7k resistors.
Does that make some kind of sense?They're the two big ones right at the end of the preamp stuff, but I can't read the values.

Yes, they would have used some caps, but I can't tell from the pic which ones. Probably the ones on the end of the board near the bridge. They would be biggg value but lowww voltage.

[frank57]

I think they're pretty much where that black wire going to the ground bolt is.
Where there are 2 x 4.7k resistors.Those are nowhere to be found on the original schematic.
You can see it a bit better in this shot.

One Hiwatt with something resembling a regular tone stack is this oddball one I found.

On that dubious Korean one I have they used something similar but the buzz hum problems on that amp seem partly
related to the Power transformer.An artificial ct seems to have brought that hum quite a bit.
Could be a total crap PT is the big problem on those amps.
Going through dropping diodes caused an imbalance in the voltage.
Does that make sense?The heaters too are done in an odd fashion.Can buzz come from there?

There is another goof the guy made with the filtering.
The bias tube should be fed from the front not the back like he did there.
I can correct it.Any harm from trying it?It's fun messing around with it anyway.