audio-talk

Another excellent event ,well done again Steve ! The quality of kit was really good and I enjoyed listening to everything. Some of the actual music was "not me" but then most of mine is "not yours" ! :oops: I had quite a few interesting conversations (hi-fi and F-1) and was very ...

Well I've changed it so the cap and cathode resistor both come off the neg heater pin. I thought it sounded a gnats better but in a blind test I doubt if the difference (if it were there) could be heard. Its now packed up in the car raring to go. EDIT I see Tentlabs reccommend that both the cap and ...

Bizzie wrote: Why did he use two diodes on each tap off the TX I've not seen that before.

This link details many different ways to rectify AC (from Hammond)

http://www.hammondmfg.com/pdf/5c007.pdf

Using two diodes instead of one increases the voltage rating.

I seem to remember on the original PT15, the cathode resistor and cap were both attached to the filament negative terminal when using DC heating.

Is there a school of thought on this ?

I've rewired one. Now we have 37.2V at neg filament and 57.5 at pos (20.3V difference) Cathode resistor to neg term 37.2V through 560R = 66.4ma & 2.5W Now checking the heater dropping resistor we are dropping 1.6V across 0.5R which is 3.2A. That sounds a bit better ! Thanks for the your advice a...

andrew Ivimey wrote:
I only stopped using it becasue it really didn't cut the mustard soundwise,

That's odd, cos I've been really impressed so far !

Lets see how the new mods work.

I'm probably confusing you Andrew (and everyone else :wink: ) No Tentlab heater modules on this ! 18v toroid - bridge - 25,000uf - 0.5R - 25,000uf - filament. The filament supply voltages are referenced to the bridge negative terminal and the voltages on the diagram referenced to the main amp star g...

Done a diagram and measured a few voltages with the amp playing mooosic..

The heater supply is floating.

Voltage first cap (before resistor) = 22.3V

Voltage second cap (after resistor) = 20.4

1.9V through 0.5R = 3.8A = 7.2W

Thinking again

If I'm loosing 2.2V through 0.5R then thats passing 4.4A = 9.68W

Does that sound right ? Wheres the extra 1.4A going ?

I'm not really with you on that Andrew ! Voltage at bridge (DC) = 22.2V so I need to loose 2.2V Assume current for GM70 is 3A 2.2V @ 3A = 0.73R and 3A through .73R = 6.6W And 3A through my 0.5R = 4.5W If my calculations (Ohms Law) are correct then 2W resistors wont do, OR am I missing something ????...

Mike H wrote:Ah right so 3.3A per 18V winding. X2

.

Yes ! I went for a 120VA cos Andrew had warned me about the problem.

They have gone from "mildly warm" to "warm" , but not HOT !

My potted heater toroids are 120VA (6.6A) 0-18 + 0-18 connected in parallel and are now mildly warm ! They were on offer at Rapid and a bit cheaper than normal. I wanted 22,000uf caps but could not find any at the right price,so I'm using a 10,000uf and 15,000uf together (25,000uf) before and after ...

That must be the bargain of the year !

Now have both monoblocks in position and working proper like. HT is 600V. Earlier I noticed the bleeder resistor heatsink on the first amp was not as hot as number 2. When I checked one of the wires from the two 6D22s rectum friers had broken, so my good initial impression was on half HT ! I am very...

Still cant get the full 20V ! With 0.5R I can only get 19.98V Post has been and no sockets, so now off into the machine shop (garage :wink: ) to make another base for monoblock number 2. Number one is playing (mono) at the moment and shows promise ! :) Filament hum does not seem to be a problem, and...