HRM needs some Lovin'

[pompeiisneaks]

For those of you that don't speak french that doucement le matin et pas trop vite l’après-midi

means "gently in the morning, and not too fast in the afternoon"

~Phil

[fred.violleau]

For those of you that don't speak french that doucement le matin et pas trop vite l’après-midi

means "gently in the morning, and not too fast in the afternoon"

~Phil

Thanks for the translation Phil!


Humble and Dumble,

Fred.

[fred.violleau]

I am on the last miles!

Finally hooking the preamp board on the chassis.


Spent too much time figuring out the OD relay and recycled the fet board in the missing part for the on board Dumbleator


Hopefully I will be done by the end of the week!


Humble and Dumble,

Fred.

[fred.violleau]

I should be done with wiring tomorrow. Any advice for the first power up? what should I be looking for?



I will use the lamp trick in front of the amp to see if there is a short.

I have a multimeter at my disposal (the small 40$ one the guys on the forum were referring to). But I do not know how I should use it... any video serving as reference on how to debug a preamp using a multimeter?

I will get my different voltages and report here. I have #183 voltages references. Should there be differences with the HRM? I suppose not.
The journey of the build is almost over. Can’t wait to start to debug and play this thing!

Thanks for the help!


Humble and Dumble,

Fred.

[pompeiisneaks]

One of my most common tests is to put my meter in continuity mode and do two things:

1. connect the black lead to ground and then test two things across the board:
a: make sure all ground connections make continuity cleanly and at very low ohms. I don't connect to the turrets/eyelets but the leads of the components. This tests not only the path to ground but any soldered connections.
b: make sure there is NO path to ground on all of the B+ and anodes of the tubes. Also anywhere else you know there shouldn't be ground, maybe at points of the grids etc.
2.get both leads and make sure you get good continuity from each pin to the lead of the connections on the board, say from the cathode pin to both leads on the cathode resistor and cap, this points again to the solder connections being good. I do this to every connection quickly to make sure I see no bad solder joints.

That has saved me quite a few times on power ups, as I've found things not getting good continuity OR getting continuity they shouldn't be.

~Phil

[fred.violleau]

Thanks for the tips Phil!


Humble and Dumble,

Fred.

[fred.violleau]

Almost there...
First power up within minuts!



Humble and Dumble,

Fred.

[ChopSauce]

Tight build

It should be tricky to review the circuit one last time before powering it

[fred.violleau]

Ok powered on unloaded and nothing smelled bad, no smoke, apparently nothing burned...

I will load with tubes and see what is happening. B+ seems to deliver but I will measure voltages on each pin and report. So far I am happy


Humble and Dumble,

Fred.

[martin manning]

Check the available bias voltage range before installing tubes, and don't forget to start with the bias at the most negative voltage and connect a speaker load when you do.

[fred.violleau]

Ok so here are a few readings with tubes loaded:
B+1 : 450v (to output transformer)
B+2 : 450v
B+3 : 431v
B+4 : 309v
B+5 : 177v (Dumbleator)
B+6 : 127v (Dumbleator)

V1a:
168v
0
1.71v

V1b:
183
0
1.70v

V2a:
185v
0
1.62v

V2b:
203v
0
1.48v

V3a (Dumbleator)
177v
1.72v
0

V3b: (Dumbleator)
87v
0
0.64v

V4a (PI)
297v
18.4v
56.3v

V4b (PI)
288v
19v
55.8v

Power Tubes 1 : 6L6
0.06v
0
454v
450v
-29v
451v

Power Tubes 2 : 6L6
0.0v
0
460v
454v
-29v
457v

I might need some help for the next stages.
Did not play a note yet.
I might do that and then see what's next

I suppose Bias is off (-29v does not seems good, I will check on the forum what value I should get)

But hey I did not burn anything so far

and now allow me to play a few notes on this thing !!!

[fred.violleau]

Tight build

It should be tricky to review the circuit one last time before powering it

Thanks ChopSauce, looks like I used a cable gage a little too big, that made the wiring a bit difficult and cluttered the available space as well...
Lesson learned for the next amp !

I did follow @pompeiisneaks's advices and measured continuity on almost everything.
I did checked twice or thrice before any soldering... Really spent a lot of time reviewing everything !

[fred.violleau]

Check the available bias voltage range before installing tubes, and don't forget to start with the bias at the most negative voltage and connect a speaker load when you do.

Thanks for jumping in Martin,

I have (not sure if I understood this correctly) on the middle lug of the bias trim pot value that goes from -27.2 up to -42.7
Is this correct?
I must say I have never biased an amp before
I will check how to on YouTube!

Edit : did try to play, and nothing is coming out of it... Amp is dead quiet no hum no nothing

When I took my measure I did hear the speaker crack so everything is not lost but I will have to troubleshoot this.

[martin manning]

Power tube pin 5's will need to be negative, at around -45V. Looks like you a reasonable adjustment range, but you might need to slide it down a bit. I'd say it goes from -27.2 DOWN to -42.7 now, and I think you'll want it to go down to -50 or more with full line voltage applied. If that measurement was made with the bulb limiter in, take it out and then remeasure. If you want to lower it, increase the resistor going to ground from the bias pot.

[martin manning]

Is your bias circuit still like this? https://tubeamparchive.com/viewtopic.ph ... 65#p380765
Do you have 1 ohm resistors on the power tube cathodes to sense current?