Those schematics are for the HS-696, I have the HS-696C, not sure what the difference is if any.
The bad news is that 160 mA. shown coming off the rectifier. 160 mA. of B+ is not enough. If the apparently substantial 6.3 VAC winding is unused, the VA gained can go into the B+ rail. A 5AR4 rectifier exhibits lower forward drop than a 5U4 and draws 2 A. of filament current as opposed to the 5U4's 3 A. 5 VA gained along with a near perfect rail voltage can't be bad. Use a Sovtek 5AR4 and 2 UF4007s as shown in the diagram provided to rectify the B+. The "raw" B+ must be taken from pin 8, as that's the 5AR4's cathode sleeve connection. A modestly valued 15 μF. film 1st filter cap., like this, will further ease the stress on the power trafo. Follow the 1st filter cap. with a Hammond 159T choke and 330 μF. reservoir part. Clamp mount the reservoir cap. in a chassis hole for air convection cooling.
We need B- power and filament current for all tubes other than the B+ rectifier. A Hammond 262A12 will provide B- power and 12AT7 heater current. 4X 6V6s, a 6H6Π (6n6p), and a 6AL5 draw 3 A. of filament current. A low cost AnTek AN-0206 easily deals with the requirement.
What has me scratching my head is why Motorola used the 250 mA. 5U4, when a 175 mA. 5V4 would have worked. Perhaps for reasons of economy of scale across models, a power trafo/rectifier combo whose capability exceeded the shown 160 mA. was used. However, we need real proof of that, before we change the thinking.
We need B- power and filament current for all tubes other than the B+ rectifier. A Hammond 262A12 will provide B- power and 12AT7 heater current. 4X 6V6s, a 6H6Π (6n6p), and a 6AL5 draw 3 A. of filament current. A low cost AnTek AN-0206 easily deals with the requirement.
What has me scratching my head is why Motorola used the 250 mA. 5U4, when a 175 mA. 5V4 would have worked. Perhaps for reasons of economy of scale across models, a power trafo/rectifier combo whose capability exceeded the shown 160 mA. was used. However, we need real proof of that, before we change the thinking.
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I actually have the Antek 6v tx you mentioned and was going to use that for the heaters. When I looked at the schematic, I was thinking that the circuit draws 160ma, but the power trans could deliver more current, it is a pretty large and heavy TX and took up most of the space on the original chassis. I was going to order the allied tx in the schematic for the B- as it is only $16. I do have pretty much and entire garage filled with new and salvaged gear, so I may already have one that fits the bill. I also have bins of just about every rectifier known lol!
AFAIK, the 6K27VF is made by Hammond for Allied. Use whichever costs less between the 6K27VF and 262A12, as they are "identical" except for filament voltage.
There is a risk in using the Motorola power trafo, but with the 6.3 VAC winding tied off things should be OK. The 5U4 is rated for 250 mA. and the 5 VAC winding had to supply 3A.
A film 1st filter cap. is an expense, but given its modest value, optimizing performance seems indicated. Modern 'lytics do pretty darned well in the ESR & ESL depts.
There is a risk in using the Motorola power trafo, but with the 6.3 VAC winding tied off things should be OK. The 5U4 is rated for 250 mA. and the 5 VAC winding had to supply 3A.
A film 1st filter cap. is an expense, but given its modest value, optimizing performance seems indicated. Modern 'lytics do pretty darned well in the ESR & ESL depts.
All PS caps will be motor run capacitors and I have a choke from a past st-70 rebuild that I could use as well. Every thing is going to be powder coated; the chassis will be "Rustic Texture" and the TX end bells will be "Alien Silver" base with "Jamaican Teal" top coat, all from Prismatic Powders. I should be able to shoot the TX end bells this weekend (hopefully). I want this amp to have a vintage look to it. I even have some cloth covered wire and a retro style 3 prong plug for the power cord coming in too.
The Dyna C354 choke is a total PoS. 😡 Both more inductance and current handling capability are needed. Hammond's 159T is an OK "off the shelf" item, but if Heyboer can wind you a 10 H./250 mA. part, at a competitive price, that's the way to go.
A good sized inductor suppresses ripple and definitely decouples the 1st filter cap. from the reservoir. We want a large rectifier conduction angle and comparatively small 1st filter cap. charging pulses. Excessive I2R heating in the "vintage" power trafo is a mortal enemy.
A good sized inductor suppresses ripple and definitely decouples the 1st filter cap. from the reservoir. We want a large rectifier conduction angle and comparatively small 1st filter cap. charging pulses. Excessive I2R heating in the "vintage" power trafo is a mortal enemy.
I have other chokes, but they are big, heavy, and take up a lot of space, plus I will be shipping this amp across the country and the shipping rates increase as weight increases.
I have a nice NOS triad 250-0-250 20ma power transformer that I could possibly use for a 6cg7 front end?
I have a nice NOS triad 250-0-250 20ma power transformer that I could possibly use for a 6cg7 front end?
Yes, well said. I guess am being over-sensitive. In my dream world, we all tap our toes to music that is made for anyone who appreciates it.
They like what they like, but who says anyone can't enjoy it...I don't really see the disconnect here? I should have used the term "Praise and Worship" music. But we should probably start a new thread in the lounge section to further discuss.
Yes, but I'm going to build an el-cheapo for my self and just go with the Dynaco A-410 schematic with a 6sn7 at the input for gain. There is no way that I will have all the necessary parts delivered in time.
Ok got most of the chassis cut. I have around 6 vintage HP Paeco 9H 125ma chokes, two of em in parallel should work out great!
Inductances in parallel, like resistances, follow a reciprocal law. Still, a net of 4.5 H. rates to be beneficial. That beats the living guano out of a PoS Dyna C354.