[Harp-L] Re: Dano Special Series D Model 68... schematic?

["Steve Rowse" <steven@xxxxxxxxxxxxxxxxxxxxxx>]

Hi. No schematic for you but here's what I sort of know. All reasoning 
herein is shaky as it's based on your info and my defective understanding, 
so read it as guesswork & take care.

On the rectifier pin 6 has I reckon no internal connection so it's likely 
being used as a convenient solder point only. Any resistors coming off that 
are likely to be B+ voltage droppers for the plates of the tubes. You'll 
need a 5 watt possibly. Reason why it's burned out - shorted filter cap 
(that's the 16mfd) or maybe internally shorted 6X5, they were famous for 
this & sometimes took out the power tranny so check that too. If the value 
lies between 600 and 1600 ohms it's not that critical but if you're going to 
guess it I'd go high rather than low, then check the voltage it's putting 
through pin1 & make sure it's something the tube it goes to can take. What's 
pin 1 connected to? If it's the power valves then 350v or so would probably 
be ok; if it's the 6SJ7 150v would be quite a lot & for harp you want it 
lower anyway - 100v? At your own risk... but I'd try a 2K 5 watt first. The 
6X5 is cheap, buy a new one before you do anything. Replace the cap too but 
don't go over 16mfd as the 6X5 won't like anything higher, that's its max 
for a first filter. And check the power tranny before that even. A Weber 
copper cap is available to replace the rectifier. Webervst.com.

Ok, about the 6V6s. Pin 1 I think is again not internally connected so is 
again likely being used as a solder tag only. This will therefore likely be 
a shared cathode resistor (esp if the pin 8s are connected to one another); 
it probably has a cap in parallel with it but maybe not. If it is a cathode 
resistor, this one you can vary to set the bias. 1500 ohms is likely to be 
(very) safely high (ie cold bias), and yes, it might go as low as 220. I'd 
use a 5 watt again to be on the safe side. Start high and work down till the 
bias is right.

Hope this helps your thinking.

Steve

Message: 24
  Date: Sat, 18 Jun 2005 10:48:39 -0500
  From: "Gary Bohannon" <beauxart2@xxxxxxxxxxx>
Subject: [Harp-L] Dano Special Series D Model 68... schematic?

Just got one of these amps, made in '55 and in incredible shape.  Looks like 
a 1x12" version of the 'Walter amp.  It has tremelo and the following tube 
lineup:

6X5 rectifier
2x6V6GT power
6SJ7
12AX7
12AX7

When I got the amp and opened it up to change the filter caps/new cord etc, 
I noticed a small resistor across pins 6 and 8 of the rectifier tube... 
burned up beyond recognition.  Tried to measure it and got readings anywhere 
from 1.6k ohms to around 600 ohms.  I need to know what that resistor is. 
One of the pins, I think 8 (?) has a 16mfd X 450 volt cap tied to it.

The other burnt resistor is between the two power tubes and ties pin 8 of 
one tube and pin 1 of the other together.  I looked inside my Silvertone 
1432 (which has a similar tube lineup using a 6X5 rectier) and noticed that 
the resistor is 220 ohm... but no resistor across the rectifier tube... 
rats!  So I think I'm halfway there...

Any help, or a schematic, would be appreciated.

Thanks in advance!

Gary B.
Nashville