“Shiny Eyes” 4P1L Gain Stage 19dB on PCB

Here is another 4P1L design. All started when I tried to figure out a gain stage for a First Watt F4. The F4 is a unity gain 25W class A power amp that needs about 14Vrms input in order to deliver max power.

4P1L offers a x9 gain. Therefore, using a 4P1L gain stage is appropriate and the input sensitivity of the hybrid amp will be about 1.55Vrms.

I built my first F4 in a 4U standard ModuShop Dissipante. seen at http://www.modushop.biz/site/index.php?route=product/category&path=66_97_107.

I had to built the 4P1L gain stage so it fits inside this case. The max dimensions were 12″x12″. I built the first one on a garolite FR4 board and attach all components and small PCB to it (see previous built https://simplepleasuretubeamps.files.wordpress.com/2014/12/photo-1-1.jpg). It was a hassle to position and attach each board to the main FR4. This led to the design of a single PCB board. I also wanted to integrate the Coleman regulators and use standard heat sinks such as the Wakefield 657-20ABP. Rod helped me figure out the size of the heatsink.

The schematic  is simple: The power supply uses 3 transformers ( one of the 187D20 for each filament, and one Antek 50VA 160V for the HT.). Ht supply is filtered by a CLC (470uF-15H-470uF). The raw supply for the filaments uses 1N5822 and CRC 10mF-0.47R-10mF. The Coleman regulators need to be preassembled except the power transistors who are mounted on 2″ Wakefield heatsinks. The 4P1L is biased at about 115V Uak, 35mA and 560mA starved filament. Th headroom in this case is about 7dB. The load for the 4P1L is a cascoded DN2540 CCS. The PCB measures 266mmx274mm. It was much cheaper to order it on 1.6mm thickness and I provided many holes for support. One can use Aluminum stand-offs to make sure that the board stays rigid.

The only concern is how the 4P1L’s socket is attached to the board. I would use neoprene damper sandwich mount, rubber rings and even a dead weight ( in the pictures I just soldered the sockets to the board but I have to remove them and use the dampers..there is a hard to notice noise that comes from the very small vibration of the power transformer and the 4P1L is very sensitive to it).

Distortion levels are very low in the 0.0x % with a predominant 2nd harmonic. The frequency response is as flat as possible in the audio band.

For anyone who wants less gain there are few options. One can use  a step down direct feed line output transformer, such as LL1671/30mA. Another choice would be to use a parafeed line output transformer , such as Jensen JT-10k61-1M.

The sound is very rewarding. The DHT is complementing the solid state push-pull, and the resulting music experience is balanced, with great dynamics and nice sounding harmonics.

overall top overall front viw delay timer top view rear top view coleman regs closeup front closeup

A possible BOM is listed below:

“Shiny Eyes” 4P1L Gain Stage (preamp) 18-19dB
Part name Mouser part# How many Price each Cost total
Toroidal AS-05T160 N/A   Antek transformers part, shipping included 1  $          40.00  $           40.00
Hammond 187D20 546-187D20 2  $          12.82  $           25.64
Thermistor CL-60 527-CL60 3  $            1.78  $             5.34
0.033uF 275V X2 80-PHE840MK5330MK03 1  $            0.36  $             0.36
1N5822 511-1N5822 4  $            0.43  $             1.72
SiC diodes 941-C4D02120A 4  $            2.26  $             9.04
IN4001 512-1N4001 1  $            0.18  $             0.18
IC555 595-NE555P 1  $            0.49  $             0.49
2N3906 610-2N3906 1  $            0.41  $             0.41
IC7805 511-L7805CV 1  $            0.48  $             0.48
DN2540N5 689-DN2540N5-G 4  $            1.42  $             5.68
5V relay 655-RTD14005 1  $            2.04  $             2.04
Trimmer multiturn 200R 72-T93YA-J-200 2  $            1.98  $             3.96
Heatsink Wakefield 2″ 657-20ABPE 4  $            1.83  $             7.32
Heatsink Wakefield 1.5″ 657-15ABPE 2  $            1.16  $             2.32
10mF 16V 598-SLPX103M016A3P3 4  $            1.82  $             7.28
470uF 400V 598-SLPX471M400H7P3 2  $            5.63  $           11.26
0.47 ohms 5W wirewound 588-TWW5JR47E 4  $            0.80  $             3.20
1000uF 16V 647-UVK1C102MPD 2  $            0.26  $             0.52
220uF 16V 598-227CKE016M 1  $            0.10  $             0.10
15 ohms 1/4W 71-RN60D-F-15 2  $            0.11  $             0.22
47 ohms 1/4W 71-RN55D47R0F 4  $            0.17  $             0.68
56 ohms 1/4W 71-RN55D-F-56 2  $            0.16  $             0.32
1ohm 1% CMF551R0000FKEB 2  $            0.88  $             1.76
1kohms 1/4W RN55D1001FRE6 1  $            0.10  $             0.10
1Kohms carbon  composite 588-OD102JE 4  $            0.70  $             2.80
100koms 1/4W RN55D1003FB14 3  $            0.10  $             0.30
1 Mohms 1/4W 71-RN55D-F-1.0M 2  $            0.10  $             0.20
220 ohms 1W 71-CPF1220R00FKE36 2  $            0.45  $             0.90
220 kohms 3W 66-GS3T0220KJ 1  $            1.01  $             1.01
10nF 100V 505-MKP2D021001BJC00 1  $            0.23  $             0.23
0.1uF 100V 505-MKS2.1/100/10 4  $            0.24  $             0.96
1uF 600V min Supreme N/A, from Parts Connection, Sonicraft etc. 2  $          20.00  $           40.00
8 ohms 20W non-inductive Radio shack 2  $            3.00  $             6.00
Loctal Russian sockets  eBay , type    PL3-5-14(or 16) 2  $            6.50  $           13.00
Hammond  158L choke 546-158L 1 23.93 23.93
Bridge rect timer 625-B250C1500G-E4 1  $            0.68  $             0.68
4P1L eBay 2  $          10.00  $           20.00
Total parts on PCB  $         240.43
Total estimated shipping costs  $           25.00
PCB cost ( depending on number ordered and supplier)..cheapest  $           30.00
Other parts ( RCA jacks, IEC main connector, Fuse socket, Mains switch, volume control(s) )…estimated  $           55.00
Enclosure needs to measure at least 12″x12″x4″…rough estimation  $         100.00
Total  $ 445.43

“Shiny Eyes” Tube active crossover, my implementation of Pete Millett’s design

“Shiny Eyes” Tube active crossover

My implementation of Pete Millett’s design

Back to work on a different type of project. I needed a 4 pole that rolls at 24dB/octave. I also needed 2 frequency crossover options: first around 100Hz and second around 700Hz. I like Pete Millett’s design at http://www.pmillett.com/tube_active_crossover.htm. He also had some boards left which was awesome. I want to thank Pete for all his support.

The PSU is a little different that Pete’s. For the high voltage, I use a quasi choke input and two sets of chokes. the last capacitors are low ESR Vishay MKP at 100uF. The PSUD2 results show a low output ripple of about 0.6mVrms.


The low voltage supply uses two LT1084 set at 6.3V output and feed each channel’s vacuum tube’s filaments. The layout of this crossover is very simple: left side, and far away from the PCB is the PSU: right side is the PCB with switches and RCA jacks. The enclosure is made of high quality Brazilian cherry top coated with light oil and urethane. The inside of the wooden enclosure is screened using a high purity 5 mil. copper sheet. I also used a screened FR4 board inside the box, between the PSU and the PCB.

top inside psu

The hard part was to figure out the switches at a decent cost. I found a guitar store that had 6 positions 4 pole rotary switches. I used four of the them, one for each 2 pole filter ( two 2 pole filters per channel). I used RN55 1% Vishay for all filters, and not only.

PCB inside

Tubes are E88CC/6922 Jan Phillips low noise from thetubestore.com.

The sound is transparent and there is no noticeable hum or noise.

Measurements, all tubes are biased at 8mA. B+/B- at 95V.

HF outputs:

HF-THD HF-600Hz cutoff HF 90Hz cutoff HF Harm H2 H3

LF outputs:

LF Thd LF FR at 90Hz cutoff LF FR 600Hz cutoff LF THD H2 H3 cutoff 600Hz

And last but not least some pictures:

top overview overview top right top left 00 top right case and plate

“Shiny Eyes” PSE 300B

“Shiny Eyes” PSE 300B


A few month ago I had long phone conversations with my audiophile friend from New Jersey who wanted to buy a 300B amp for his new field coil speakers. He looked at the Audio Note PSE 300B, but had an itch for Monolith Magnetics transformers. I offered to help him design and build a PSE 300B.

And here is the final product, result of a few month of talk, design, breadboard, wooden enclosures ( I made them myself…my grandfather was a skilled carpenter and I learned few basic things from him) and final assembly…and now enjoy listening for a while at least…

This amp was designed in same manner like my PSE 4P1L: separate enclosure for PSU, top plate ( CNCed at Front Panel Express) will hold all parts and sub-assemblies, generous slots for heat management, symmetry across the board for a nice “stereo” look, very attentive to detail regarding the optimum placement of all components.

This is my first amp designed using 300Bs and I can say that I am very happy with the sound result. It has the power reserve that PSE 4P1L lacks of.

Few design strategies: self biased final stage ( as my friend asked to have a free of adjustments amp), driver and first stage with minimum 6dB overhead, all DHTs amp, all Monolith Magnetics power and audio transformers, all high quality components.

Few words to describe the schematics:

  • Main
  • Final stage parallel 2x300Bs Princess Sophia B/c with separate self biased provided by equivalent 1Kohm 36W ( 3x3K MRA 12) resistor parallel with 220uF/100V Cerafine capacitor.
  • Driver 4P1L loaded on the interstage Monolith IT-01 gaped for 30mA, self biased using equivalent 0f 3.75Kohms/ 24W ( 2×7.5k MRA12) parallel with Cerafine 220uF 200V ( 4x 220uF/100V series/parallel)
  • First stage CX-301A loaded on Ale’s Gen II gyrator Mu output DC coupled to 4P1L. 01A is filament biased on 20 ohms MRA12 resistor
  • 8x Coleman filament regulators provide supply at constant current for all DHTs
  • SSHV1 is used to provide supply for the driver-input stage
  • PSU
  • PSu is providing unregulated, well filtered DC high voltage. The circuit uses 6CJ3 tube rectifiers and CLCLC filtering. Because of the high cost of the audio transformers, I provided a HT fuse.
  • There are 8 raw supplies, one for each Coleman regulator. The schematics of the raw supply is according to Rod’s documentation, providing low enough ripple.
  • two 11 wires flexible umbilical cords carry all the LV and HV, and Ground from the PSU to the Main.

I used my minimal equipment to make some measurements ( I am using a scope, an interface and Audiophile 192 sound card, ARTA software).

Here are few results:

  • FR : 10Hz-20kHz =/- 0.5dB
  • Input sensitivity for 16W on 8ohms output: 0.8Vrms
  • THD at 12W on 8Ohms output : 3%
  • Driver THD at 16W output: 0.2%

THDvsPower PSE 300B

Here are some more pictures:

Coleman regulators on 300x75mm heat sinks

fil regs

More from design stage and woodwork

design stage psu-enclosure-and top plate Main enclosure and top plate UmbilicalCords

Inside the belly of the beast ( each enclosure weights around 80 lbs.


More pictures

Main close up inputs close up left whole amp overview on top on

close up left

Some temperature measurements:
300B bias resistors Temp

And finally schematics and top plates:

top plate psuMain schematics PSu schematics top plate psu

I want to give thanks to Ale Moglia for his awesome gyrator , Rod Coleman for his great regulators and his advises and Yves at Monolith Magnetics for his permanent support.

I also want to gives thanks to my friend who gave me the opportunity to build such an expensive amp.

Facts: Weights total of 160 lbs and draws about 500 W.

“Shiny Eyes” CX-301A Line stage

all side 2

Here is another preamp that is using the amazing 01A tube. It has a very pleasant sound that will not fatigue your senses even when played for long hours.

This is an  DHT preamplifier/ line stage using the tungsten filament Cunningham CX-301A tube.  I has one stage and is built with separate enclosure power supply.

The power supply unit uses Hammond 270BX for main HV in a CLC configuration -47uF(Obbligato Film-Oil)-15H(75mA)-47uF(Obbligato Film-Oil). HV is supplied with a low ripple which is perfectly adequate considering that SSHV will add at least 60-80dB PSSR bringing the ripple at extremely low levels ( I could not measure with my equipment).  The raw power supply for the filament bias are using Hammond167L12, 1N5822 and 10mF-2x1ohms-10mF-0.1uF-220pF. PSU is supplying all voltages (HV and LV) through a 7 wire umbilical cord, which is permanently attached on the main preamp side and can be disconnected on the PSU side. However, it is not recommended to run the PSU without load because of the risk of damaging the preamp when reconnect the umbilical cord.

The main preamp uses one stage CX-301A in filament bias, DC input and transformer coupled output. It uses the Lundahl LL2745/PP that is working great for 3-6mA single ended. The main preamp enclosure incorporates the SSHV and two Coleman filament regulators. The 01A is filament biased at 7V on 30 ohms at 230mA.  The secondary of the LL2745 is using either Alt Q (2.8:1)or Alt R (5.6:1) providing two fixed gain alternatives. A 6 pole two position rotary switch is facilitating this function. The preamp is provided with volume control. I installed individual stepped attenuator by Gold Point ( a very good price quality solution).


The following measurements are only to give you a sense  of the approximate performance. I used a computer software and interface and this comes with some artifacts and noise that are not present when the amp is connected in a audio path. One, if owns high quality audio analyzer, can take more precise measurements

  • Gain : Alt R: 3-4dB(x1.5) and Alt Q: 9-10dB(x3)
  • Input impedance: 80kohms, unbalanced
  • Output impedance measured comparing output on Z load (523K and 300pF) and (10k and 300pF)

Alt R: 437 ohms

Alt Q: 1750 ohms

  • Power consumption: about 50W

“Shiny Eyes” 01A Line stage Measurements

  • LL2745 Alt R  6:1       
  • FR 20Hz @ -1dB, 20kHz @-1.5dB,  12Hz-27.5 kHz @ -3dB


  • THD at 2.9V output (1.92Vrms input) Gain 3.58dB, 2nd @ -75.5dB bellow fundamental, 3rd @ -73dB


  • LL2745 Alt Q 8:1       
  • THD at 5.83V output (1.92Vrms input) Gain 9.65dB, 2nd @ -73.3 dB bellow fundamental, 3rd @ -72.7dB


  • FR 17Hz @ -1dB, 42kHz @+1 dB,  one dip at 11kHz @-1.6 dB


Recommended Operating Mode: Alt R or 3dB gain position. Reason: the 3 dB gain has a very good frequency response and low output impedance, consequently providing the best sound. The 9dB gain option was provide in case there is not enough gain in the audio chain and there is no other alternate option.

More pictures:

topPlates topPlate_box wooden_KevinVancouver psu top back main front all side top back2  back 1 top trafo no cover top trafo no cover wiring

Preamp/linestage, switchable between 01A and 26 type tubes

side view

This is an all DHT preamplifier/ line stage.  I has one stage and is built with separate enclosure power supply. This a very flexible solutions preamp. One can choose from:

  • 01A or 26 type tube
  • line output transformer or capacitor coupled output
  • two level of gain on transformer output

The power supply unit uses Hammond 270Ex for main HV in a quasi choke input 0.68uF(MKP)-20H(100mA)-47uF(Obbligato Film-Oil)-20H(100mA)-47uF(Obbligato Film-Oil).

Here is the PSUD2 result:


in reality the rectifier used was 6BY5GA so the above results are slightly different. HV is supplied with a low ripple which is perfectly adequate considering that SSHV will add at least 80dB PSSR bringing the ripple at extremely low levels ( I could not measure with my equipment).  The raw power supply for the filament bias are using Hammond167L12, 1N5822 and 10mF-2×0.33ohms-10mF-0.1uF-220pF. PSU is supplying all voltages (HV and LV) through a 7 wire screened umbilical cord, which is permanently attached on the main preamp side and can be unplugged on the PSU side.

The two raw filament supplies are placed in the PSU enclosure and are providing the following :
– PSU raw filament supply for 26: biased at 900mA. Output 15V, ..no more than 10.3V supplied after Coleman that is 9V on 10ohmsRAwFil 1

Same PSU when switched to 01A ( biased at 230mA), will provide at least 12.5V after Coleman or 7.1 V on 30 ohms bias resistorRAwFil 2-01AThe main preamp incorporates the two SSHVs and four Coleman filament regulators ( one pair for 01A and one pair for 26). In order to switch between 01A and 26 tubes, there are 2 sets of DTDP high quality Carling switches. Three of the poles are used to switch between the Coleman regulators ( each channel has one Coleman filament regulator for the 01A @ 230mA and one Coleman filament regulator for the 26 @ 900mA) and the fourth pole is switching the bias resistors placed between one of the filament pins and signal ground ( a permanently connected 30 ohms Mills MRA12 is used to bias the 01A and when switching to the 26 tube there are 2 more 20 ohms Mills MRA12 added in parallel to the 30 ohms( equivalent bias resistor for the 26 will consequently be 7.5 ohms)).

The other feature of this preamp was to switch between transformer output and capacitor coupled output. An additional DPDT Carling switch will do the job. One section (pole) of the switch will be connected to the anode of the tube and connect the anode to either the primary of the line output transformer (LL2745) or the Gyrator ( Ale Moglia’s Gen 2 ).  The secondary of the LL2745 is using either Alt Q (2.8:1)or Alt R (5.6:1) providing two fixed gain alternatives. A 6 pole two position rotary switch is facilitating this function. There are two sets of RCA Neutrik jacks, and in order to use either transformer or capacitor outputs one needs to physically move the interconnection cables to the appropriate jack.

The preamp is provided with volume control. I installed a stereo stepped attenuator by Gold Point ( a very good price quality solution).


The following measurements are only to give you a sense  of the approximate performance. I used a computer software and interface and this comes with some artifacts and noise that are not present when the amp is connected in a audio path. One, if owns high quality audio analyzer, can take more precise measurements

  • Gain when transformer output T out) : Alt R: 3-4dB(x1.5) and Alt Q: 9-10dB(x3)
  • Gain when capacitor output (C out): 18-20dB(x8)
  • Input impedance: 80kohms, unbalanced
  • Power consumption: max 85VA

“Shiny Eyes” switchable 01A-26  Line stage Measurements

  • 26 type vacuum tube
  • Transformer output
  • LL2745 Alt R  6:1   
  • THD at 3.03V output (1.92Vrms input) Gain 3.58dB, 2nd @ -66dB bellow fundamental, 3rd @ -68dB
  • THD-T-R-26
  • FR 14Hz @ -1.5dB, 21kHz @-1.5dB,  8Hz-29 kHz @ -3dB


  • LL2745 Alt Q 8:1       
  • THD at 5.93V output (1.92Vrms input) Gain 9.8dB, 2nd @ -66.3 dB bellow fundamental, 3rd @ -67.4 dB


  • FR 6Hz @ -1dB, 37kHz @+1 dB,  one dip at 11kHz @-1.35 dB


  • Gyrator load and capacitor coupled output
  • THD at 16.83V output (1.92Vrms input) Gain 18.8dB, 2nd @ -66.3 dB bellow fundamental, 3rd @ -67.4 dB


  • FR 12Hz – 41kHz @-0.25 dB


  1. CX-301A type vacuum tube
  • Transformer output
  • LL2745 Alt R  6:1     
  • THD at 3.1V output (1.92Vrms input) Gain 4.16dB, 2nd @ -66dB bellow fundamental, 3rd @ -68dB


  • FR 20Hz @ -0.7 dB, 20kHz @-1.7dB,  7Hz-25.5 kHz @ -3dB


  • LL2745 Alt Q 8:1       
  • THD at 6.2V output (1.92Vrms input) Gain 10dB, 2nd @ -66 dB bellow fundamental, 3rd @ -69 dB


  • FR 6Hz @ -1dB, 37kHz @+1 dB,  one dip at 11kHz @-1.35 dB


  • Gyrator load and capacitor coupled output
  • THD at 17.6V output (1.92Vrms input) Gain 19.2dB, 2nd @ -66.1 dB bellow fundamental, 3rd @ -98 dB


  • FR 8Hz – 43kHz @-0.5 dB


  • Output impedance measurements
Output type/tube 26 tube CX-301A tube
C out 260 ohms 457 ohms
T out 4dB 413 ohms 462 ohms
T out 10dB 1,656 ohms 1,886 ohms

And here are some more pictures:

top view topplate psu Main-with copperview Mainbottom psucloseup psubottom psutop topplateMain



18dB Gain CX-301A preamplifier to feed the First Watt F4

This is my implementation inspired by Ale Moglia’s 01A preamp Gen2 (http://www.bartola.co.uk/valves/dht-pre-amplifier/01a-preamp-gen2/). The plate gyrator is Ale’s design and it works like a charm. I want to thank Ale for his great dedication to bring this gyrator to high performance levels. I am using a Dynamicap 0.22uF in place of C1 and a 0.47uF Mundorf Supreme for C2. I also tried the FT3 0.22uF and like it better than the Supreme…I made the boards for smaller caps and couldn’t fit it in there.

Here is the schematics I used:


I chose the filament bias resistor of 30 ohms in order to raise the headroom to 8 dB so the preamp can be used from a standard 2Vrms source. I am using the extremely good, latest version  of Coleman regulators adjusted to 0.25A. The reason I am not using starved filaments is first to lower the output impedance and second that I could not notice a big improvement in microphony from 250mA to starved at 200mA.

The power supply is overdesigned by added SSHV just in case I want to add a line output transformer and make it switchable from Gyrator mode ( 18dB gain and about 1K output Z) to LL2745/PP 5.6:1 mode ( 3dB gain and lower Zout about 400 ohms).

I designed the layout as always  preferred ( when there is no issues with complete screened enclosure) : one top plate ( Aluminum 1/8″) that has all the components attached to, and one wooden enclosure. In this case there are no heat management issues so I had to drill less holes on the top plate. Usually I like to use Front Panel Express to order the top plate ( for a more professional look and easy to assembly)..this time I just draw it in CAD and printed out to use for exact drilling locations. The top plate is standard 12″x12″( McMasterCarr)  and consequently the wooden case is 13″x13″x3.5″.

The 01A sockets are attached to the top plate using neoprene vibration damping sandwich mount ( type 9241K41 at McMasterCarr).

CX-301A preamp measurements March 14th, 2015

I am happy with the results of today’s measurements. The tables below show results for THD and FR.

Channel Input voltage 1kHz (Vrms) Output voltage (Vrms) THD(%)
Right 0.5 4.1 0.015
1 8.4 0.033
1.93 16.1 0.064
Left 0.5 4.1 0.008
1.04 8.8 0.016
1.93 16.6 0.034
Channel Frequency (Hz) Level (dB V/V) Roll off (dB)
Right 8.8 16.45 0.53
20 16.05 0.13
1,000 15.92 0
20,000 16.3 0.38
30,000 16.45 0.53
Left 8.8 14.4 0.55
20 13.98 0.13
1,000 13.85 0
20,000 14.26 0.41
30,000 14.51 0.66


I can conclude that the preamp has a maximum gain of about 8.5 for a THD of 0.033% where the second harmonic is dominant at about 70dB below the fundamental and more than 20db above the following harmonics. These results are expected and the distribution of the harmonics shows that the sound of this preamp should be extremely pleasant. Indeed the sound of the CX-301A has some magical touch specific DHT’s and even beyond expectations.

I am using it right now to supply to a mini F4 recently built. The reason I have built this preamp is because of the F4. It has no problem driving the F4. It also can be used to feed a low gain power amp if the input capacitance is in the lower hundreds of pF.

I am extremely impressed with the sound of 301A and definitely this will be a keeper. Again some pictures:

Some early development:

close up 01A Early breadboard test with Gyrator Ales designbreadboard2 breadboard1

Layout design: designstage

overview inside inside sockets inside psu2 inside psu inside 1 top no tubes 2 top no tubes top 2 straight top front case bottom case

6H30 preamp and mini F4 integrated

All started after I built  and listened to the First Watt F4 and liked it very much. The original F4 has 6 power mosfets per channel, draws about 160W and weights about 35 lbs, delivering 25 current buffered W per channel at 8ohms (2.58Ax2.58Ax8 ohms/2= 26.6 W). Then I built the Mark Audio 7.3A speakers and thought of pairing them with an amp that will deliver enough power to listen up to 90 dB levels. From my previous experience with the 4P1L – F4 integrated, I learned that a 16-20 dB gain it is plenty to drive the F4. The output impedance of the 6H30’s is even lower than the 4P1L’s, so no issues of driving capability nor gain. Actually I needed a little more gain as my small FLAC player has a lower output compared to a CD player. I chose 6H30 for multiple reasons: very linear, low Rplate, good gain and overall low PSU demands. PSU uses Antek 160V/50VA main transformer, FRED rectifiers, choke 157G and a 555 based 30 seconds HV time delay circuit. A hand made PCB holds the noval socket, the RC cathode bias, the grid resistors and the coupling caps. Separate PCBs are used for each anode load DN2540 based cascode CCS. 6H30 runs at about 125V/20mA.

I used a standard aluminum enclosure from Ebay and modified the top plate to fit all the pre-amplifier components. The (so called) mini F4 has only 4 power mosfets per channel and each runs at 300mA…this provides a 1.2×1.2×8/2=5.76 W pure class A with the heatsinks at reasonable temperature. At this size of the enclosure (wxlxh 9.5″x10″x5″) everything fits tight and weights 20 lbs. I am very happy that it fits well on my working desk.

The combination of the Mark Audio MTL Alpair 7.3A (design by Bob Brines) and the Mini F4-6H30 pre integrated sounds awesome: great dynamics specific to F4, low distorsion from the 6H30 and pleasant sound from the Alpair ( lows are excellent enough considering the size of the driver, mids are well defined and highs are awesome..this driver can go up to 30kHz…very unique).

F4 6H30 preamp side CCS F4 6H30 board F4 6h30 PSU 6h30 top F4 6h30 psuF4 F4-6h30 side F4 6h30 front F4 6h30 back