New SET.....

Runs a bit warmer than some of my other amps....but coupled with my Altec Model 14 it sounds wonderful!!!
I am just getting acquainted with it....been spenind the past days listening to it's smaller brother the 205a mkII
 

paulbottlehead

Active Member
Be sure to have a look at the cathode bypass caps on the inside. The last one of those that I worked on had cooked its cathode bypass caps since it uses mixed bias. I ended up replacing them and relocating them further away from the cathode resistors.
 
I agree the baby A205 SEP EL84 amp MK II with upgrades as well....quite a lovely little amp. Has amazing 3-d quality to the sound-stage.
I think my only observation is that it has a lot of "gain" with the volume control, hardly turn it past 9 o'clock on the dial, but then my speakers are pretty efficient.almarro.jpg
 

Audionut

Next Round Is On Me
I have tried to get hold of a 205 for several years but they rarely appear on the used market in Sweden as the owners of these stubbornly refuse to let them go!
We have at least a three Almarro owners on the Haven, and I’m still hopeful one will sell theirs soon as these don’t come up for sale stateside often either. :)
 

Ernie

Me
I have the first version, one of the first to arrive from Japan, when Venus HiFi was the national distributor. When the designer/builder Yoshihiro Muramatsu came over from Japan, for an AKFest, he brought a pair of speakers that he designed and built for the a205a. I got that hand-built pair of show speakers, when he didn't want to take them back. That combination took me off the acquisition path.

I took my a205a up to @billfort's, for a listening session with him and @prime minister. Hooked up to those beautiful Altecs, the almarro held its own, and then some. Even Bill was surprised.

Ray Logan (rayneman), his memory for a blessing, had a 318A and paired it up with Grumpy's Audio Note E's, at an early Fest. That room was the site of an infamous all-nighter. The perpetrators shall remain nameless. :zip
 

Andyman

Junior Member
I remember the carnage of that night and saw the aftermath, but my brief time there was earlier in the evening...:D
 

paulbottlehead

Active Member
this seems to be a solution to the problems with early almarro A318 / A318B and blown cathode bypass capacitors, this is taken from a discussion on a european audio forum, any technical knowledgeable person who would like to explain in more detail what this is about ??
(constant current sinks / sources (CCS's)??
View attachment 35390
My assumption with the one I worked on was that the cathode bypass caps blew from being overheated, as they were super close to a giant wirewound resistor that otherwise was also very hot and cooking off its own lettering. The grid leak resistance was 100K IIRC which

These amps run mixed bias, meaning there is substantial resistance between cathode to ground but also adjustable negative grid bias. It's tough in a 6C33 amp to run cathode bias, as you may need 80V of bias at 200mA, so the resistor will dissipate 16W. This really requires a 50W resistor and some decent space/ventilation. Almarro instead develops less of the bias across a cathode resistor and the rest is obtained by negative grid bias.

If the grid to ground resistor is too large of a value, the grid voltage can wander, which also causes the bias to wander. If you put a CCS under the cathode of the 6C33, you can fix the current and as that grid voltage moves, the cathode voltage will move with it to maintain proper current. The issue with this is that the CCS will get super duper hot if that voltage grows too large.
 

Audionut

Next Round Is On Me
My assumption with the one I worked on was that the cathode bypass caps blew from being overheated, as they were super close to a giant wirewound resistor that otherwise was also very hot and cooking off its own lettering. The grid leak resistance was 100K IIRC which

These amps run mixed bias, meaning there is substantial resistance between cathode to ground but also adjustable negative grid bias. It's tough in a 6C33 amp to run cathode bias, as you may need 80V of bias at 200mA, so the resistor will dissipate 16W. This really requires a 50W resistor and some decent space/ventilation. Almarro instead develops less of the bias across a cathode resistor and the rest is obtained by negative grid bias.

If the grid to ground resistor is too large of a value, the grid voltage can wander, which also causes the bias to wander. If you put a CCS under the cathode of the 6C33, you can fix the current and as that grid voltage moves, the cathode voltage will move with it to maintain proper current. The issue with this is that the CCS will get super duper hot if that voltage grows too large.
So you’d not recommend buying one? If I do, would spacing out the caps away from the resistors be sufficient? I’d hate to have to redesign the thing. Really wanting to try a single ended el84.
 

paulbottlehead

Active Member
The EL84 one is not going to suffer those same problems.

On the 318, yes, move the cathode bypass cap as far away as is reasonable. I believe when I rebuilt the one I had on my bench, I sought out capacitors made for high temperature environments just to be on the safe side.
 
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