The Amp Garage

Thank you all for the input. YOu are confirming my impressions. THe orger if going out for a new OT. My 1st option is to go to heyboer and ask for the "Metro spec" but I am open to suggestion here. Also, if someone has one they would like to sell Thank you again ! Why not just use twice the intende...

... I have always been under the impression the higher the impedance the lower the output power, all else being the same. That's pretty much the deal for solid state amps. They have very low output impedance, very low loss in the output devices such that the output voltage signal can swing almost r...

...eg run a continuous tone around the onset of clipping through the amp... How to determine the onset of clipping without a scope? And if a scope is available, then why not measure power into the load directly? Good point, the onset of clipping might not be audibly obvious, especially with this ty...

More accurate results might be achieved if the calculator I linked previously was used. Especially if voltages under load are used. eg run a continuous tone around the onset of clipping through the amp and measure the V DC at the OT CT, at the screen grid HT supply node (other leg of the 4k7 HT drop...

Hi Pete, The OT is a Classictone 40-18037 18 watt Marshall type. The spec sheet shows the reflected impedance to be 9.2K with an 8 ohm load (the Weber currently in there is 8 ohm) and 8.2K with a 7 ohm load and the Jensen was closer to 7 ohms which is what I used to obtain the readings posted. ... ...

I suggest to connect it to the nearest convenient point of the chassis metalwork, eg a solder lug at its valve socket fastener.
By that, any RFI nasties it picks up will be kept as far separate from the amp circuit as is feasible.

I think your Blue would be fine, with 280V across the 6V6 it's not going to put out more than 10W.
Trying putting the numbers into a calculator eg https://www.vtadiy.com/loadline-calcula ... alculator/
The relevant output power is shown after 'at g1=0:'
Do you know the OT primary impedance?

The power amp feedback loop block is set up as a non-inverting operational amplifier, signal input to the non-inverting input, feedback signal (ie a sample of the loop output) to the inverting input.
See https://www.electronics-tutorials.ws/opamp/opamp_3.html

A bad connection between valve pin and its corresponding socket female contact seems a likely suspect here. Most likely V3 and most likely the one for pin 2.

For those who aren't members of the ssguitars forum, I've copied the info nosaj posted there 26 April Just fyi I messes up the ssl certs and trying to get them reinstalled to get both sites back up. My apologies. nosaj 4 May I'm restoring a backup now. I've just been so busy withe school and work. H...

... I think Pete Farrington / @pdf64 might have some knowledge in this area. Thanks, I suppose I can come across as convincing, but this discussion shows me up as being something of a dilettante :roll: Helmholtz's secondary leakage inductance measurements are great. When combined with a global feed...

The negative feedback network here is essentially a potential divider. The 820R negative feedback series resistor option doesn't seem a good idea. Combined with a 5k shunt resistance, it allows far too much feedback, 0.86 of the speaker voltage will appear at the LTP 2nd grid, which will greatly red...

There's the design centre to design maximum apples to oranges thing muddying the water.
A 200V design maximum limit would be perhaps 180V design centre.
Tied up with that is older and more recent info, RCA is 1959, GE 1955, TungSol is a 1959 print of 1948 info.

Raoul Duke wrote: ↑Sat Apr 19, 2025 9:26 pm the resistors weren’t giving me a reading

Where were you putting the meter probes?