Blueman2

@ang728, at first I thought your picture of the blown SiC was one of my photos! Pretty much exactly the same pattern. See below. Hoping the Cree I am now using will fare better.

The Blue Hawaii lives! Got my shipment of Cree C2M1000's and replaced the 4 parts that appeared bad. Turns out the BC557B was not bad. I had just tested it incorrectly. So just the c2m1000, the 24V diode, and the 2N3904. My guess is that the alternate part I used for the C2m1000 was not quite up to the task and the inrush current of the startup finally killed it. I will probably replace the positive PSU's chip as well since I got 5 of the C2M1000's for future repairs as needed. I had not adjusted the balance of the amp since I first built it, and decided to check the voltages. After 30 minutes warm up, balance and offset are still +/- 1V. Impressive given the number of hours I have put on that amp over the past 3 years.

mwl168, great to hear from you! It blew just as the HV power delay relay clicked on (I have a 45 second delay after LV and filaments turn on before HV turns on). So probably an inrush current issue if there was no short.

Good thought, Kerry. I checked but the resistance levels on the negative side are about the same as positive side for the amp boards. PSU itself does not show a short. I plan to rebuild the PSU, test it on the bench at low input voltage, then ramp it up. Could just be one of the silicon devices was weak and took the others along with it.

Hello all! Long time since I have posted here but I continue to lurk. I just had the negative power board go out on my Blue Hawaii. The c2m1000 literally blew its top off. 3 other components also bit the dust in the process. Parts are ordered and will replace in next couple days. All other parts appear to test OK. Looking at the parts that failed, any ideas on the cause or which part failed first that led to the others failing? And more importantly, are there any parts you recommend I replace regardless of how they test, given the mode of failure? The Amp had been working great over the past few years, though with the Carbon and my trusty old SRX Plus, it sometimes went several months between uses. EDIT: I just recalled that I did the build when the C2M1000 was out of stock, so used the SCT2H12NZGC11 from Mouser listed in my Feb 2021 post in this thread (right hand column below). Maybe that was the issue?

I think so. However, I am not sure that the shunt PSU was ever finalized. I recommend going with one of the GRHV variants for the power supply. But the SRX itself remains a great, simple to build amp.

Ah. Very ingenious!

Whaaat? Did you hack apart a TO-247 casing to put that SMD into it? Insane. 😄

What is your setup for creating boards? Do you use a small CNC router?

Nice.

@JoaMat, what is it for?

I have successfully used the ROHM version (3rd column in the list above) for over a year in the Carbon amp with no issues, but I think that part is also out of stock? Used the one if the first column (which has good availability now) in a GRHV with no issues, but not on a Carbon. But from the specs, it should work as well as the other two.

I applaud this thread!!! On point 1 that James made, I am very guilty of helping cause this issue. I have mixed comments on the GRHV across threads for Blue Hawaii BJT, Carbon, and a few others as well. Just to make sure that it is almost impossible for anyone to learn from what I did. 😁 On point 2, I have tested 2 alternatives to the C2M1000170D, and both appear to work fine. One of them is pretty new and usually in stock: https://www.mouser.com/ProductDetail/?qs=vHuUswq2%2Bsy%2BS7yfkaWaCA%3D%3D Item on left is the one that is in stock. Item to the right is the alternative that I successfully used as well, but often not in stock. Middle is the standard part which appears to be quite elusive.

Yes, this baby will keep you warm in the winter. I ended up doing the same, starting with 17mA and then increasing to 20mA after it was running for a couple days. Not sure it really made much difference in either sound or heat production, but just wanted to push the envelope.

[embarrassed] Yes, yoke. [/embarrassed] Sigh.

@Pflugshaupt, thanks for sharing pics! Love the old school volume knob. And the woodwork looks wonderful. There is something different about your SR-007's. Is that a custom yolk?

Doh, sorry Pars. I did not see the min order quantity. The only part that appears in stock at Mouser that might be compatible is https://www.mouser.com/ProductDetail/?qs=vHuUswq2%2Bsy%2BS7yfkaWaCA%3D%3D Item on left is the one that is in stock but has not been tested. Item to the right is the alternative that I successfully used. Middle is the standard part.

Pars, there is a replacement/alternative for the C2M that I found and used successfully in my build. Let me find that part number. EDIT: Here is a link to my post: Here is the part: 755-SCT2H12NZGC11 Unfortunately, it also appears out of stock, but it is an alternative that worked for me in my Blue Hawaii and is still going strong, if you can find it elsewhere. EDIT2: I just checked my supply of parts and have none of the SiCs. Sorry. EDIT3: TTI appears to have some of the ones I used: https://www.tti.com/content/ttiinc/en/apps/part-detail.html?partsNumber=SCT2H12NZGC11&mfgShortname=ROH&utm=ECIA

@simmconn, First, that is a great looking build. Can you share pictures of the internals? Curious how you crammed all that into such a small space. As for the hum, a few thoughts: 1. You are using separate transformer windings for the 6SN7s and the 12AT7s, right? 2. Have you tried to elevate the filament heaters as described in the thread? That eliminated my hum Nice build!!!

@hhobeika, great build! Very impressed with your details such as keeping the signal output wires parallel and flat just like in the headphone cable. I love those little details!

Neat! When you say your bias is only able to reach 490, how are you measuring that? You cannot just measure with a normal DMM as it's own impedance will give a false low reading. And where did you get the board made? Looks quite nice.

I did this build about a year ago. I have used Antec for all 4 of my builds so far and have been very happy with them. Antec is very conservative with their VA rating, so I would not worry so much about that. As for the voltage, I think they spec their voltage at 115, but not sure. It will say on their site for each transformer. You then have to look at your normal line voltage. For me, I typically am at 122 to 124 volts AC here in San Francisco area with PGE. So my 300V transformers typically give me 320VAC under load. But YMMV depending on local AC voltages.

I had the same thoughts come up when I ordered mine. I ended up going with smaller (in voltage and in VA) simply because that is what would fit in my case. If space is not an issue, I think your choices are good.

I will also put in a recommendation for Antec. Here is what I used for my Carbon: AN-0215 - 25VA 15V Transformer $11.00 USD AS-2T300 - 200VA 300V Transformer $38.50 USD

@mwl168, I found exactly the same thing. Once I elevated the heaters, the hum was eliminated completely. 12AT7s are at 60V (voltage divider off B+ rail) , and 6SN7s are at -340V (tied directly to B- rail). In all, I did 4 things to make mine totally silent: Used voltage divider to elevation the filament voltages. +60V for 12AT7s and -315V (or in my case, I just tied it to B- so -340V) for the 6SN7s I switched to different set of tubes. The ones I started with just hummed. After switching, much less hum More careful grounding of components Finally, to get rid of slight hum when volume control was at 11:00 to 5:00 position, I switched from a 50K pot to a 10K pot, which totally eliminated any hum when the volume control was in the mid/high region.