Metropoulos Forum

Hello everyone I was lucky enough to stumble on an unbuilt kit from around 2008, It is a 100 wtt Plexi replica. I am a novice amp "builder" but have a pretty extensive background in electronics, mostly from my aviation days way back when.

Well I put this thing together in about seven days and I am pretty proud of it......except......My voltages are a bit screwy...

It has the Mercury Magnetic s upgrade Transformers, and there are a few things that are not quite right.

V1 pin one has a voltage of close to 300VDC, The heaters are right at 3.25 VAC and V1 does not get warm like the others, The voltages at the power tubes are about 458VDC, and the Bias is -45 when I follow the instructions.
I have swapped out different tubes same story. I don't leave it on long because of this errant voltage.

There is a hiss from the speaker. I am going to to rewire the tube socket. And see from there

I have video snippets of this build on you tube here; http://www.youtube.com/user/emergencynu ... ature=mhee" onclick="window.open(this.href);return false;

Not much to glean off, just me gloating, but you can see that its a clean build, I think I followed the instructions exactly.

Any help would be appreciated, I can tell that this thing will be a tone monster, once I get it sorted.

I am beginning the think its supply.....

Thanx Vic

Never mind, its fixed....what good is an amp builder that can't troubleshoot his own mess?

It was a wire that had some of it plastic insulation interfering with the pin. Sounds amazing!

This was a kit that was un-built by its original owner since 2008, I lucked upon it.......Thanx for providing a great kit! I really enjoyed doing it.

Vic

Well, I don't know who to ask this....

I found a few mistakes and cleaned them up. While I was in there, I wanted to be sure to rebias the tubes, as the instructions state. I have about an hour or so playtime on it.

The original voltage on pin 3 of V-4 to V7 was 458VDC during the test phase, that is 40 volts below the charts designated voltage of 498 using Metroamps Transformers, I have the Mercury Magnetics upgrade, I understand that these voltages vary. OK....

So tonight I recheck everything and now the Voltage is 447VDC, I rebias the tubes. [I have yet to listen to it...]

The question is; When should I worry about that voltage? It is more than 50 volts low....is there a % or limit?

The other DC voltages are commensurate with the 447VDC.

Any insight would be appreciated.

VIc

Is there anyone out there?

The Mercury Magnetics PT probably has different specs compared to the Metro-Heybor one so that's why you see a different rectified voltage. As for the drift from 458vdc to 447vdc some of it could be attributed to the 120vac wall voltage fluctuating in combination of things "settling in". If nothing appears obviously wrong just keep an eye on it by re-checking the voltages to see if it stabilizes.

sct13 wrote:Is there anyone out there?

Good question.

Low voltages can't hurt your amp. Most important thing is how does your amp sound? For EL34's, If you bias your amp with 65% of max plate dissipation your bias should be reading around 35-36mA with a B+ of 447-458 dcv. That is a good number for you.

Look at the "Hi" bias number for the SL68 in this pic (.034) https://www.dropbox.com/s/5og36yddsy63bsi/SL68.jpg" onclick="window.open(this.href);return false;. This SL68 is probably running around 470 dcv.

Watched your yt vids. I don't hear anything wrong with that amp. The voicing sounds good.

Thanx for the replies,

Its at 451VDC, with a little playing it has actually come up a little....It was 440VDC at one time.

One other thing that surprised me, was the tubes that came with the kit. They would not bias past 26mV. The pot was cranked all the way. So I put in an older set and they went up to 70mV (briefly) also the Plate voltage different. After screwing around with that and some other circuit changes (just to learn what does what) I returned it all back to stock including the tubes. And it sounds killer now. The tubes are at about 34mV. Not sure what happened there. The Lar Mar install went without a hitch and its plexi heaven.....Time for another......How does one get a kit nowadays, I stumbled on this one....

Thanx for watching the YT vids...Keep on the lookout, I got real 68' 50 watter....Will be doing some comparative analysis

sct13 wrote:Thanx for the replies,

Its at 451VDC, with a little playing it has actually come up a little....It was 440VDC at one time.

One other thing that surprised me, was the tubes that came with the kit. They would not bias past 26mV. The pot was cranked all the way. So I put in an older set and they went up to 70mV (briefly) also the Plate voltage different. After screwing around with that and some other circuit changes (just to learn what does what) I returned it all back to stock including the tubes. And it sounds killer now. The tubes are at about 34mV. Not sure what happened there. The Lar Mar install went without a hitch and its plexi heaven.....Time for another......How does one get a kit nowadays, I stumbled on this one....

Thanx for watching the YT vids...Keep on the lookout, I got real 68' 50 watter....Will be doing some comparative analysis

Glad to hear everything worked out even if you were never able to pin point exactly what caused the problem(s). As for a kit, you kinda have to make it up yourself from parts available from Valvestorm's offerings and George's stuff (transformers). So what's the deal on your 68 50w? Got any pictures you can share?

sct13 wrote:Is there anyone out there?

I got as far as the 'never mind it is fixed' post - which was misleading