Hiwatt Electronics

I have been working on my Biacrown 50 watt Hiwatt head and looking at it pretty closely with my new 4 channel scope. Since I bought it, it has been updated as follows:


  1. Replaced power electrolytics. These are not easy to find for the high voltages involved and I was able to find some from a German manufacturer.
  2. Replaced three control potentiometers that were scratchy.
  3. Replaced diodes in the power supply. I did not have diodes with high enough peak inverse voltage, so I replaced the original hiwatt installed diodes with two UF4007 diodes in series.
  4. Replaced original power transformer with a Hammond 290GX. Hammond did not have a power transformer designated for a 50 watt Hiwatt, so I used the one for a JCM800. I had the necessary windings and was designed to drive two EL34 tubes.
  5. Replaced the output transformer with a Mercury Magnetics HI50-O. The transformer it came with was not a Partridge, so it was neither collectible nor notable.

Summer of 2021 I decided to take the amp to the next level with a few more upgrades.

  1. Power transformer HI50-P from mercury magnetics–expected to be better to some degree. I am curious to see if it helps with a low level 60 cycle hum that comes out of the speaker. This transformer has taps for the other voltages this amp supported originally including 100, 120, 230, and 240 volts. This amp was designed to be able to tour Europe and the United States without the need for voltage adapters. It also has a center tap for the filament windings which may help with the 60 cycle hum. The Hammond had a tap for this as well, but inexplicably, I did not connect it to ground.
  2. Output transformer HIO50-M from mercury magnetics.. This is their best transformer designated for a 50 watt Hiwatt.
  3. Replaced the electrolytic cap used in the bias circuit.
  4. Replaced the diode used in the bias supply with a UF4007 fast recovery diode. Its a fast recovery diode and I had it an extra laying around.
  5. Replaced the power supply diodes. Upon review, I discovered that it was not best practice to have two diodes in series without a resistor or cap to ensure there was no voltage-hogging that might burn one out. I determined this diode needed at least 1250 volts of PIV rating. I learned there are not a lot of diodes available for these high voltages. After ordering a diodes that Digi-Key did not have in stock, I changed my order to two Vishay SF1600 avalanche/fast recovery diode. These have PIV rated at 1600 volt. These diodes are spherical in shape and are the size of a matchhead. Everything powered up as normal after these changes. The upgrade was more for safety than an expectation of an audible difference. There is lots of debate as to whether fast recovery diodes make and audible difference, but they are just a few cents more, so why not? I also believe this was the only sort of diode I could find that exceeded 1400 PIV.
  6. Replaced the screen grid resistors with 1K/5 watt resistors, based on the recommendation of Steve Fischer, late of Trainwreck amps. He believes the higher rating provides better protection for the amp. I note the old resistors were 100 ohm/1 watt. The Hiwatt schematics typically have a 1k resistance on the schematics, but apparently at one time, 100 ohms were used. I have read that 1K protects the tubes from excessive screen grid current, at the cost of only a watt or two of power.
The Hiwatt is a bit different from typical guitar amps in that the guitar signal goes straight into the first pre-amp tube and the volume control comes after this stage. This has two 1/4 inch inputs, termed ‘normal’ and ‘brilliant’. The circuitry after the first preamp tube (V1) reduces the low frequencies from the brilliant stage. To view the performance of this tube, I put a 1,250 HZ square wave into the guitar inputs (Grids, Green trace), and took the signal from the plates of these tubes (Blue and Yellow). The corners of a square wave contain lots of harmonics, so to pass the square wave this cleanly, this preamp stage is very high bandwidth–far exceeding the audible range. After this, the signal is put into tone shaping and will be much changed from its original form. I note the particular tube I have (12AX7) has uniform gain in both stages and this stage has a voltage amplification factor of 62, quite satisfying.
This screen capture examines power supply ripple. The yellow is called HT1 in the schematics (High Tension 1 using the British tension to mean voltage). This goes straight into the output transformer and supplies the power stage. It has 4.32 volts of ripple and the 120HZ sawtooth wave to be expected from a full wave rectifier. It sits at 480 volts DC while the amp is idling. The purple trace is taken at HT2, which is 100 ohms away from HT1, and has additional capacitance to filter it. The benefits are clear as the ripple here is 440 millivolts, about 1/10 that of the HT1. HT2 is sent to the screen grid. Its voltage is 477 volts. The blue trace is taken from the power tube grid bias supply and has a frequency of 60hz due to the half wave rectifier that powers a single capacitor. This power supply has minimal current draw and is able to limit ripple to 78 Millivolts.

Grandpa’s property ownership in Lennox, South Dakota

When I was born, my grandparents Bessie and Adolph, on my mother’s side, lived in Lennox, South Dakota. As a child, my brother and I visited them a few times a year, and spent a week or so at their house which was my parent’s vacation. We used to sleep in the summer on their screened in porch. At first the vey loud cricket chirping and occasional train activity, a hundred yards to the south, kept us awake, but ultimately it lulled us into the deepest and most refreshing sleep imaginable. But grandpa’s house had one magical quality for me, the likes of nothing I could have imagined as a child–he had a 4 car garage full of wood an tools, and I spent countless hours tinkering away in there. I have thought a lot about their lives in Lennox, and much of that information is lost to me. I thought one thing I could do, at least, was use land title records to put some context to their lives in Lennox.

First of all, a little about Lennox. I believe the town was created as the result of the Milwaukee Railroad creating a train station at that location, and it is named after a railroad executive. In an agricultural community, a train station was a place where farmers could bring their harvest so it could be sold and transported to mills or food companies. Large storage silos, called grain elevators, were built by the tracks to store the grain until it could be loaded onto railroad cars.

Regarding land titles: Platting is the process whereby a developer takes a large piece of property, often farmland or forest, and records a plan in the title records which lays out parcels of property and roads. While a parcel would initially have been referenced to government survey boundaries, the legal address of properties in the platted land are references to lots within the plat. This will become clear later when we get down to the details. For the purpose of my grandparents in Lennox, there are only two plats of interest: Lennox (Or at times Lennox Original), which contains downtown Lennox in the south side of the railroad tracks, and Jacob’s Addition, just north north of the railroad tracks.

To give a flavor of the legal description land referenced to government survey boundaries, the legal description of the land comprising Lennox Original is N.E. 1/4 Section 32 Township 99 North, Range 51 West. More detail on this government survey scheme can be found on the web. For our purposes, the legal description simply refers to the original boundaries assigned by federal surveyors as the result of the Land Ordinance of 1785. I will note that in the lands west of the Mississippi, most chains of title begin with a federal grand to individuals in the 1860s as part of the homesteading process. The Lennox Original plat was filed November 5, 1879, and the Jacob’s Addition plat on May 12, 1884. At this time, South Dakota was a Territory, not a state. Statehood occurred on November 2, 1889.

Below are excerpts of the plats Jacob’s Addition (north of the railroad tracks and above) and Original Lennox (south of the railroad tracks and below). The highlighting indicates my grandparents property ownerships, with the residential house on the left and the trailer park on the right. The storefront for the Frosty Freeze is in downtown Lennox.

Jacob’s Addition

The Frosty Freeze

Grandpa first entered the title records of Lennox on September 12, 1952 with the purchase of the West 26 feet of lot1 and 2, block 11 City of Lennox (Lennox Original Plat. The deed does not record the purchase price. There was a $2,000 ($20,200 in 2021dollars) mortgage for this property. This was a storefront on Lennox Main Street. This was a commercial property, and I believe my grandparent’s ran some sort of dairy service company as well as an ice cream shop.

Visiting my grandparents at the Frosty Freeze. 4 1/2 months old.

They exited this business, and sold the property on April 13, 1972. I am not able to determine the sale amount.

The House

On September 12, 1953, they purchased at auction, lots 1, 2, and 3, block 13, Jacob’s addition. This property faced main street. The house and yard comprised three lots of the plat, and was 150 feet square. When visiting their house, we could see the grain elevators and railroad tracks to the south from their yard. Between us and the railroad property was a residential home (now a business), and a commercial building with junk inside. I never saw any sort of activity in that building in the 1960s when I was a child there. The original house was torn down over the years and a new house placed more in the center of the lot. The original sidewalk is intact, and of the 4 car garage, only some partial brick wall remains.

Grandpa developed cancer, and on September 30, 1983, they sold the property and moved to an apartment in Sioux Falls. I can’t determine the proceeds of the home sale.

The Trailer Court

With the encouragement of the Mayor of Lennox at the time, Grandpa purchased “The north 19 feet of lots 5 and 9, and all of lots 3, 4, 10, and 11. This was a contiguous piece of land across the street and 100 feet south of their residence. It was 119 feet on the north/south dimension and 300 feet on the east west dimension. On this land was a trailer park which grandpa operated as a business and maintained. I recall little about it except vague memories of one or two times when I accompanied him on a visit there where he would perhaps fix the hinge on a gate or some other repair.

They sold this business on June 19, 1978 for $30,000 ($123,000 in 2021 dollars). During a visit in 2020, I noted that the park had appeared to expand south all the way to the railroad tracks. The northern part of block 12 had some sort of farm equipment dealership when I was a child, and a similar business there today.

Uncle Glen’s House

Bessie’s brother, Glen (actually a grand-uncle) lived with them in Lennox for many years. There was a small lot and house to the west of their residential land. On December 29, 1973, they purchased this house, The east third of lots 7, 8, and 9 in block 13 of Jacob’s addition, with the purpose of fixing up for Uncle Glen to live in. He was tragically killed in 1974 in a traffic accident, and the property was sold August 29, 1979. This house stands in its original location in Lennox today.